Hydrothermal and
b
-glucanase effects on the
nutritional and physical properties of starch
in normal and waxy hull-less barley
N.O. Ankrah
a, G.L. Campbell
b,*, R.T. Tyler
c,
B.G. Rossnagel
d, S.R.T. Sokhansanj
eaDepartment of Animal Sciences, Washington State University, P.O. Box 646351, Pullman, WA 99164-6351, USA bDepartment of Animal and Poultry Science, University of Saskatchewan, 72 Campus Drive,
Saskatoon, SK S7N 5B5, Canada
cDepartment of Food Science and Microbiology, 51 Campus Drive, University of Saskatchewan,
Saskatoon, SK S7N 5A8, Canada
dCrop Development Centre, 51 Campus Drive, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada eDepartment of Agricultural and Bioresource Engineering, 57 Campus Drive, University of Saskatchewan,
Saskatoon, SK S7N 5A9, Canada
Received 9 November 1998; received in revised form 5 March 1999; accepted 22 June 1999
Abstract
Cereals having a waxy (high amylopectin) starch type may offer advantages for animal feed associated with heat processing characteristics and/or starch digestibility. Nutritional and physical characteristics of starch were evaluated in hull-less barley cultivars having a normal or waxy starch type (228 and 55 g kgÿ1
amylose, respectively). Broiler chicks (192) were fed one of eight diets in a 222 factorial arrangement from 3 to 21 days of age. The dietary factors included: (1) normal or waxy starch type barley; (2) pelleted (758C, 160 g kgÿ1
total moisture) or meal form; and (3) with or without addition ofb-glucanase. The pelleted diets were reground to remove any physical aspect of feeding pellets. There were no differences in body weight gain (BWG), feed intake (FI), feed-to-gain ratio (F/G) or intestinal starch digestibility due to starch type, nor were treatment interactions significant (p> 0.05). Feeding waxy starch barley resulted in higher digesta viscosity than normal starch barley, which was attributed to its higherb-glucan content. Fecal digestibility of waxy starch was 10% higher (p< 0.05) than that of normal starch. Pelleting did not affect BWG, FI, or F/G, but reduced (p< 0.05) digesta viscosity by 45% and increased starch digestibility by 17% in non-enzyme supplemented diets. b-Glucanase addition improved BWG, FI, F/G, and starch
Animal Feed Science and Technology 81 (1999) 205±219
*Corresponding author. Tel.: +1-306-9664128; fax: +1-306-9664151
E-mail address: leigh.campbell@usask.ca (G.L. Campbell)
digestibility (p< 0.01), and eliminated the high digesta viscosity otherwise associated with feeding the waxy starch diets in meal form.
Starch characteristics during heating were examined with 11 hull-less barley samples (5 waxy and 6 normal starch types) using a Brabender Viscoamylograph. Waxy starch hull-less barley exhibited peak viscosity10oC lower than did normal starch, exhibited a higher peak viscosity, paste instability and a lower cold-paste viscosity (negative set-back). Waxy barley may offer advantages in feed processing associated with lower gelatinization temperature, as indicated by superior pellet hardness in a model pelleting system over a range of added moisture levels and temperatures. The waxy trait did not compromise chick performance when diets were supplemented withb-glucanase.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Hull-less barley; Starch; Feed; Pelleting;b-Glucanase
1. Introduction
Barley has historically been considered a less desirable cereal grain for poultry due to its low energy content. Recent developments that have increased acceptance of barley as a poultry feed have been the widespread use of dietary enzymes (b-glucanase; Campbell and Bedford, 1992), and the development of hull-less cultivars. Dietary b-glucanase relieves the viscous state that arises in the intestine (Salih et al., 1991) with solubilization of b-glucan originating from the endospermal cell wall in barley. Nutrient digestibility and absorption, as well as feed intake are reduced, and in the case of starch, its digestion is shifted distally in the small intestine (Hesselman and Aman, 1986). The production of `sticky feces' in poultry due tob-glucan also poses litter handling problems and adverse effects on the environment of intensively housed poultry.
A second development has been the introduction of hull-less barley genotypes, in which the hull is shed during harvesting. This increases the metabolizable energy content by removing the dilution effect of the fibrous hull. While b-glucan levels are affected by both genetics and environment, early hull-less barley cultivars were notorious for containing high b-glucan, and this occurrence likely prevented their adoption prior to widespread application of dietary enzymes (Campbell et al., 1993). With enzyme supplementation the effect of varyingb-glucan level is minimal, although plant breeders have purposely selected for moderate levels in current hull-less barley varieties.
Both hull-less and conventional barley genotypes occur as waxy types, in which the starch consists almost entirely of amylopectin (970±1000 g kgÿ1), as opposed to normal types containing 750±850 g kgÿ1 amylopectin with 150±250 g kgÿ1 amylose (Ullrich et al., 1986). Amylopectin is more susceptible toa-amylase than amylose suggesting that waxy starch may be more digestible than the normal starch type. High amylopectin/waxy starch gelatinizes at a lower temperature compared to normal starch, which could have obvious benefits in the production of pelleted feeds, since the benefit of cooking could potentially be achieved with lower temperatures with reduced destructive effects on other nutrients (e.g. lysine).
The objectives of these experiments were to determine the effects of heat and moisture on the physical properties of starch in waxy and normal starch type hull-less barley, the
effects of limited heat and moisture treatment (pelleting) on site and extent of starch digestion, and to determine the relative response to dietaryb-glucanase addition in broiler chicks.
2. Materials and methods
2.1. Hull-less barley samples
Eleven hull-less barley cultivars were used in the study (Dr. B.G. Rossnagel; Crop Development Centre, University of Saskatchewan, Saskatoon, SK, Canada) representing normal (six cultivars: 025; 032; 034; 035; 036; and 038) and waxy (five cultivars: 026; 027; 028; 029; and 037) starch types.
2.2. Broiler chick feeding trial
Two hull-less barley cultivars representing a normal (034) and waxy (037) starch type were available in sufficient quantity for evaluation in broiler chick diets. The effect of pelleting or meal form of barley based diets, with or withoutb-glucanase addition was examined in broiler chicks. Variables examined were body weight, body weight gain, feed conversion, digesta viscosity and intestinal starch digestibility.
2.3. Experimental allocation and management
Commercial strain day old broiler chicks were fed a commercial diet for three days. The chicks were weighed after the third day and randomly allocated to eight dietary treatments. Each treatment was replicated (cages) six times with four birds per replication (two males and two females, 192 chicks total). The broiler chicks were housed in battery brooders and given feed and water ad libitum throughout the experimental period (3±21 days).
2.4. Diets and feeding
A broiler starter diet (Table 1) was formulated based on two hull-less barley cultivars, containing normal (278 g kgÿ1
amylose, 58 g kgÿ1
b-glucan) or waxy starch (55 g kgÿ1
amylose, 73 g kgÿ1
b-glucan) type. Each of the normal or waxy starch hull-less barley diets was divided into two portions. One portion was steam (160 g kgÿ1
total moisture) pelleted through a 5 mm matrix at 75oC (Superior Separator, Process Machine Div., Hopkins, Minnesota). The other portion was not pelleted (meal form). The pelleted diets were reground to a meal form using a hammermill without a screen to remove any effect due to form differences between the normal and waxy type hull-less barleys. The pelleted or intact portion was fed with (+) or without (ÿ) a commercial b-glucanase enzyme addition (derived fromAspergillus niger). The enzyme was added to the meal or reground pelleted diets. The enzyme preparation was added after pelleting to avoid any potential confounding attributable to partial enzyme inactivation with heat.
2.5. Response criteria
During the experimental period, weekly data collection and calculation included body weight gain, feed-to-gain ratio. At the termination of the experiment, starch digestibility was determined at the proximal small intestine (PSI), distal small intestine (DSI) and feces. PSI was defined as the region from the gizzard to Meckel's diverticulum and DSI, from Meckel's diverticulum to the ileo±ceco±colic junction.
2.6. Intestinal digesta collection
All the chicks were starved for 14 h (overnight) prior to trial termination and fed again early the next morning in order to ensure the presence of sufficient digesta for analytical purposes. Two hours after feeding, broilers from each treatment were sacrificed by cervical dislocation, dissected, and the digesta collected. Following thorough mixing, one portion of the pooled digesta sample (4 birds per replication) was taken for viscosity determination immediately, and the remainder transferred into sealable polythene bags and immediately frozen in liquid nitrogen (ÿ208C ) for later determination of starch digestibility. The birds were taken sequentially by treatment replication in order to assure treatment differences were not confounded by differing time periods after feeding. Table 1
Composition of basal diets (g kgÿ1air dry basis)
Ingredient
hull-less barleya 610.0
soybean meal (480 g/kg CP) 313.0
canola oil 40.0
limestone 15.0
dicalcium phosphate 14.8
salt (iodized) 2.5
DL-methionine 1.2
L-lysine±HCL 0.5
Vitamin±mineral premixb 3.0
Calculated analysesc
metabolizable energy (MJ/kg) 11.96
crude protein 240.0
calcium 10.3
available phosphorous 6.9
lysine 13.0
methionine 5.5
aWaxy or normal cultivar. Hull-less barley diets were given with or without enzyme supplementation at
1.0 g kgÿ1. Aspergillus niger, GNC Bioferm, Saskatoon, SK; to provide 1000 b-glucanase units per kg
manufacturer's specification; unit is total reducing sugars (glucose equivalent) released per 10 min at 308C and pH 4.0.
bVitamin±mineral premix provided the following per kilogram of diet: vitamin A, 9000 IU; vitamin D3,
1500 IU; vitamin E, 20 IU; vitamin K, 1.5 mg; riboflavin, 5 mg; pantothenic acid, 11 mg; niacin, 24 mg; folic acid, 0.75 mg; biotin, 0.1 mg; choline, 500 mg; vitamin B12. 0.012 mg; zinc, 60 mg; copper, 5 mg; manganese, 60 mg; selenium, 0.1 mg.
cCrude protein calculations based on analysed value; other values were calculated.
2.7. Measuring viscosity of intestinal contents
A portion of the pooled digesta of intestinal digesta from chicks on each treatment was centrifuged for 10 min using a micro-centrifuge (1200grpm at 25oC) immediately after collection. The viscosity (centipoise, cps = 0.01 dynes scmÿ2) of the supernatant solution was determined using a Brookfield digital viscometer (Model LVTD VCP-II, Brookfield Engineering Laboratory, Soughton, MA) at 24oC and a shear rate of 5±22 sÿ1.
2.8. Measuring starch digestion
Chromic oxide (5 g kgÿ1
) was added to all the diets for the determination of starch digestibility at PSI, DSI and excreta regions. The marked diets were fed throughout the experimental period. Prior to digesta collection, excreta samples were collected daily from each pen, frozen (ÿ10oC), and the daily collections pooled.
The pooled, frozen excreta samples were dried (60oC for 24 h), and the digesta samples lyophilized. Feed and the dried excreta and digesta samples were ground (1 mm screen). Chromic oxide concentration in feed, digesta and fecal samples was measured (Fenton and Fenton, 1979). Dry matter (DM) of digesta was determined as difference in weight between fresh and lyophilized samples and DM of feed and feces was determined according to AOAC procedures (AOAC, 1990). Starch determination was according to the procedure of Bjorck et al. (1987), in which starch is solubilized, digested using
a-amylase followed by amyloglucosidase, and quantified as glucose released (glucose oxidase method).
2.9. Starch characteristics during heating
The cooking and pasting characteristics of starch in waxy (5 types) and normal (6 types) hull-less barleys were evaluated using the Brabender viscoamylograph (C.W. Brabender Instruments, South Hackensack, NJ, USA). Characteristics measured were gelatinization temperature, peak viscosity in Brabender units (BU), viscosity at 958C (BU), viscosity at 958C for 30 min, and viscosity on cooling to 508C. The viscoamylograph (700 cm/g sensitivity cartridge) was equipped with a 500 cm3 bowl rotating at 75 rpm. The samples were weighed on a moisture-free basis and mixed with distilled water to form a slurry (80 g kgÿ1w/w). Mercuric oxide was added to the slurry to inhibit all enzymatic activities. The slurry was equilibrated in the viscoamylograph at 308C for 30 min, and then heated to 958C, at the rate of 1.58C per minute, with constant stirring. At 958C the paste was held for 30 min with continuous stirring (holding period), then cooled (setback period) for 30 min (508C). The consistency profile of the entire pasting cycle was traced on a chart recorder (amylogram).
2.10. Pellet hardness
A model pellet die was constructed to measure pelletability of small samples at variable moisture and temperature levels (Department of Agricultural and Bioresource
Engineering, University of Saskatchewan). The pelleting unit consisted of a single bore die (130 mm effective length) with an internal diameter of 6.4 mm. The unit was insulated and temperature controlled. The pre-heated, conditioned ground grain samples were placed in the pre-heated die (708, 808, or 908C) and forced against the die end (plunger diameter 0.60 cm) at 772 kg load. The conditioning process consisted of placing the ground sample (0.5 g) in a test tube (16100 mm), adding the appropriate moisture (0, 30, or 60 g kgÿ1) as distilled water with a 25ml pipette, mixing, sealing with rubber stoppers, and allowing equilibration (30 min) in a hot oil bath set at the desired temperature.
Six pellets were produced per treatment combination. These were cooled and stored until pellet hardness determination. Pellet hardness (vertical orientation) was measured using an Instron 1011 Automated Material Testing System (Instron, Canton, MA).
2.11. Statistical analysis
The general linear model (GLM) procedure for SAS (SAS, 1989) was used to analyze body weight gain (BWG), feed intake (FI), feed efficiency (F/G), intestinal and excreta starch digestibility in a completely randomized design with 222 factorial arrangement. Pens were used as experimental units, with six pens per treatment. Student-Newman Keuls (SNK) test was used to detect differences among treatment means. Only interaction means were presented because of the strong interactions present in much of the data. Pellet hardness in response to moisture, temperature, and starch type were analyzed using multiple regression procedures (REG).
3. Results
3.1. Composition of waxy and normal starch hull-less barley
The composition of normal and waxy starch hull-less barley genotypes, with reference tob-glucan, starch, viscosity, amylose (per cent of total starch), and crude protein, are presented in Table 2. Total starch and crude protein did not differ appreciably between the two barley types, whereasb-glucan and extract viscosity were generally higher with the waxy barley. The samples of waxy and normal hull-less barley used for the feeding trial were, in general, representative of the two groups.
3.2. Broiler chick performance
The dominant effect in terms of broiler chick performance was the response to dietary enzyme supplementation, which increased body weight gain and feed intake, and lowered feed conversion (p< 0.01; Table 3) for both waxy and normal hull-less barley diets, whether fed as mash or pelleted (reground) diets. There were no significant differences (p> 0.05) in body weight gain, feed intake, or feed conversion (F/G) of broiler chicks in response to feeding waxy or normal starch hull-less barley. Higher numerical mean values
Table 2
Chemical composition and viscosity of hull-less barley genotypes with normal or waxy starch type
Composition Hull-less barley genotypes
normal starch waxy starch
025 032 034 035 036 038 X, SD 026 027 028 029 037 X, SD
b-Glucan (g kgÿ1, as fed) 54 73 60 40 40 50 52
13 80 73 72 70 73 732
Starch (g kgÿ1, as fed) 620 640 624 564 642 631 619
28 571 592 600 620 632 60324
Amylose (g kgÿ1starch) 254 220 280 260 220 250 247
23 60 60 62 60 60 573
Crude protein (g kgÿ1, as fed) 151 140 144 143 140 150 144
5 160 141 142 152 150 14806
Viscosity (cps)a 103 269 762 22 76 501 289290 179 818 171 446 845 492330
aBarley cultivar coding.
N.O.
Ankra
h
et
al.
/
Animal
F
eed
Science
and
T
ech
nology
81
(1999)
205±219
for body weight gain and feed intake were observed for chicks fed the normal starch hull-less barley in the absence of dietary enzyme, but no consistent effect was evident in the presence of dietary enzyme. Feeding the pelleted feeds (reground) did not significantly affect body weight gain, feed intake, or feed conversion in comparison to the mash feeds. The treatment yielding the best performance results (body weight gain, F/G) was the normal starch hull-less barley diet fed to broiler chicks as mash with enzyme supplementation.
3.3. Digesta viscosity
Initial statistical analysis indicated that the magnitude of the effect of dietary enzyme was overwhelming (p< 0.01) in reducing digesta viscosity in relation to any effect of starch type or processing. Digesta viscosity was 10±30-fold higher for both the waxy and normal starch hull-less barley in the absence of dietary enzyme, and differences in variability within treatments indicated a similar range. To delineate the effects of starch type and pelleting the data were separately analyzed for treatments with and without enzyme supplementation (Table 4).
Digesta extract viscosity generally increased from the proximal to the distal small intestine in the chicks fed diets without enzyme supplementation, reflecting b-glucan solubilization and/orb-glucan concentration with assimilation of digestible nutrients (i.e. starch, protein). With enzyme supplementation digesta viscosity was uniformly low in the proximal and distal small intestine. Among the non-supplemented treatment groups, digesta from chicks fed waxy starch hull-less barley diets was more (p< 0.01) viscous in the proximal small intestine (PSI) compared to the normal hull-less barley isotype. Pelleting reduced (p< 0.01) viscosity of digesta in the PSI by 45% in both hull-less barley types.
Table 3
Effect of feeding normal or waxy hull-less barley as pellets (reground +) or mash (ÿ), with (+) or without (ÿ)
b-glucanase supplementation on broiler chick (21days) body weight gain, feed intake, and feed conversion
Starch
22) indicated treatment effects as follows: body weight gain, enzyme (p< 0.01); feed intake, enzyme (p< 0.01), starch typepelletingenzyme (p< 0.05); feed conversion, enzyme (p< 0.01).
bStandard error of mean.
cMeans in the same column followed by different letters differ significantly (p< 0.05).
3.4. Intestinal starch digestibility
Overall, starch digestion as reflected by the excreta analysis was high, with a sequential progression noted from the proximal to the distal small intestine, to the fecal content (Table 5). The major factor affecting starch digestion was enzyme supplementa-tion, which increased starch digestion throughout the PSI and DSI (p< 0.01), and to a lesser extent, in the fecal analysis. The region of starch digestion was affected more so than the overall level; with enzyme supplemented groups achieving equivalent or better starch digestion in the PSI than non-supplemented groups did in the DSI. Normal or waxy hull-less starch barley (non-pelleted) did not influence starch digestibility in the PSI and feces (Table 5). However, normal starch was more digestible (p< 0.01) than waxy starch in the DSI, largely as a result of the low starch digestibility of the non-pelleted waxy barley without enzyme addition. This was primarily due tob-glucan differences rather than starch type, since there were no significant differences in starch digestion (DSI) in the presence of b-glucanase. Pelleting increased starch digestion (p< 0.01) in both the PSI and DSI, irrespective of starch type. The pelleting effect was not evident in the excreta, indicating that the overall effort of pelleting was to shift starch digestion anteriorly. Waxy hull-less barley was numerically more digestible at the excreta level.
b-Glucanase supplementation significantly (p< 0.01) increased starch digestibility in the PSI, DSI and feces. The greatest response was seen when diets were pelleted and supplemented with enzymes. The effect of pelleting and enzyme supplementation on starch digestibility was more pronounced in waxy starch than normal starch. Since all barley diets would normally be enzyme supplemented, it is noteworthy that there were virtually no differences in starch digestibility among treatments at the DSI and feces (Table 5).
Table 4
Viscosity of digesta from small intestine of broiler chicks fed normal and waxy hull-less barley pelleted (reground +) or mash (ÿ) with (+) or without (ÿ)b-glucanase supplementation
Starch type Pellet Enzyme Viscosity (cps)a Enzyme Viscosity (cps)a
PSIb,c DSIb,c PSIc DSIc
Normal + ÿ 102be 390 + 10.3 9.1
Normal ÿ ÿ 254be 316 + 8.9 11.8
Waxy + ÿ 276be 376 + 8.7 10.3
Waxy ÿ ÿ 475ae 504 + 9.0 9.9
SEMd 53.1 140.6 0.8 1.2
aCentipoise.
bProximal (PSI) and distal (DSI) small intestine. cAnalyses of variance (2
22) indicated response to dietary enzyme was highly significant (p< 0.01). Because of large error differences among treatments with and without enzyme addition the data was re-analyzed (22). Viscosity in the PSI was affected by starch type (p< 0.01) and pelleting (p< 0.01); other treatment effects were not significant (p> 0.05).
dStandard error of mean.
eMeans in the same column followed by different letters differ significantly (p< 0.05).
3.5. Cooking and pasting characteristics of barley starch
The characteristics of normal and waxy starch in barley in response to heating as a barley flour slurry, as measured by the viscoamylograph are presented in Table 6. The results for a typical normal and waxy starch hull-less barley as an amylogram are depicted in Fig. 1. The viscosity units in this case refers to resistance of the hull-less barley slurries encountered by a central stirring device as the slurry progresses through pasting and ultimately gel stages. The viscosity is reflective of starch granular and molecular changes occurring during heating and subsequent cooling. There was Table 5
Intestinal and excreta starch digestibility of broiler chicks fed normal and waxy hull-less barley pelleted (reground +) or mash (ÿ) with (+) or without (ÿ)b-glucanase supplementation
Starch type Coefficient of starch digestibility
pellet enzyme PSIa,b DSIa,b excretab
Normal + + 0.793abd 0.951ad 0.963ad
aProximal (PSI) or distal (DSI) small intestine. bAnalysis of variance (2
22) indicated treatment effects as folloes: PSI, enzyme (p< 0.01), pelleting (p< 0.01), enzymestarch type (p< 0.05); DSI, enzyme (p< 0.01), pelleting (p< 0.01), enzymestarch type (p< 0.05); DSI, enzyme (p< 0.01), pelleting (p< 0.01), starch typepelleting (p< 0.05), starch type
pelletingenzyme (p< 0.05); excreta, enzyme (p< 0.01), starch type (p< 0.05).
cStandard error of mean.
dMeans in the same column followed by different letter differ significantly (p< 0.05).
Table 6
Mean Brabender pasting characteristics of starch in waxy and normal hull-less barley flours (with mercuric oxide)
Normal 95.0 594 595 348 718 +123
SDc 0.0 150.8 152.1 48.2 97.5 95.7
essentially no change in slurry viscosity as the temperature was increased from 308to 808C, after which the slurry viscosity of the waxy barley increased rapidly, peaking (gelatinization temperature) at 868C in comparison to 958C for barley with normal starch. The peak viscosity attained with the waxy hull-less barley was higher than that attained with the normal starch hull-less barley. With continued stirring at 958C, the viscosities of both barleys declined, ultimately reaching a plateau. In proportion to peak height, the decline for the waxy starch samples was much greater than the normal starch samples. However, the viscosity in the plateau region continued to be higher for the waxy starch. Upon cooling, the plateau regions were initially maintained, after which only the normal starch elicited higher paste viscosity, eventually higher than the peak height attained during gelatinization. This is conventionally expressed as `set-back', which is calculated as the difference between the endpoint viscosity and the gelatinization peak. Thus, normal starch less barley exhibited positive set-back, whereas the waxy starch hull-less barley exhibited negative set-back.
3.6. Pellet hardness
Pellet hardness for normal and waxy starch hull-less barley was assessed at three moisture and temperature combinations, as depicted in Fig. 2. Waxy barley pellets were significantly (p< 0.01) harder than normal starch barley, as described by the equation
y=ÿ6.43 + 1.99 (barley type) + 1.76 (moisture) + 0.14 (temperature) (r= 0.66**). Barley type was represented by waxy (1) or normal (0) starch. Both moisture level (p< 0.01) and temperature (p< 0.01) positively affected pellet hardness. More complex models incorporating curvilinear and interactive elements either did not improve hardness prediction significantly, or the magnitude of the improvement was small. It was noteworthy that pellet hardness differences were most apparent at low moisture conditions.
Fig. 1. Viscoamylograms of normal and waxy hull-less barley flours (with mercuric oxide).
4. Discussion
The development of hull-less barley has resulted in a crop that is more compatible than conventional barley with the nutrient-dense feeds preferred in monogastric feeds, especially by the poultry industry. A second possibility in the refinement of hull-less barley for feed may be the incorporation of the waxy starch trait for improvement of feed processing characteristics, and possibly the rate or extent of starch digestion. Changes in starch physical properties in response to heat and moisture are conventionally measured for baking and industrial applications using a viscoamylograph, although the specific relation between such results and the feed pelleting process have not been established. In the present study, waxy starch hull-less barley underwent gelatinization (i.e. achieved peak viscosity) at 98C lower than did conventional barley. Although the difference in gelatinization temperature was somewhat less than previously reported (12% vs. 20%; Goering et al., 1973), the results were comparable. The higher peak viscosity (`pasting peak') for waxy barley is indicative of swollen starch granules, which resist movement due to physical contact among adjacent granules in the starch paste and is reflected as a higher paste viscosity (Schoch, 1969). Since the molecular weight of amylopectin is greater in waxy than in normal starch (DeHaas and Goering, 1972; Zobel, 1984), granular expansion may be greater as well. Similar results have been reported previously comparing normal and waxy barley (cv. Compana) starches (DeHaas and Goering, 1972; Goering et al., 1973).
The lower gelatinization temperature of waxy starch potentially offers several advantages in feed processing. Greater plasticity of waxy starch could reduce energy input, lower mechanical effort in pellet production, and higher gelatinization (at an equivalent temperature) could improve adhesion and pellet hardness. Although starch does not undergo gelatinization during conditioning prior to pelleting in the true sense, it Fig. 2. Pellet hardness of normal and waxy hull-less barley pellets at various added moisture (M, g/kg) and temperature (T) levels (treatments 1, 2, 3M= 0;T= 708; 808and 908C, respectively; 5, 6, 7,M= 30;T= 708, 808, and 908C, respectively; 7, 8, 9,M= 50;T= 708, 808, and 908C, respectively.
seems reasonable to expect that the general relationship between waxy and normal starch would hold true during the initial stages of starch gelatinization, or starch `melting' (Thomas and Van der Poel, 1996). This interpretation was supported by the model pelleting system employed, in that there was a linear relationship between pellet hardness and temperature at all moisture levels, and equivalent pellet hardness with the waxy hull-less barley (calculated from pellet hardness prediction equation) was achieved at 14.28C lower than the normal starch hull-less barley.
Achieving equivalent pellet hardness at lower temperature would also reduce damage to heat-sensitive dietary components, for example dietary protein or feed additives. Although the present study only considered conventional pelleting, it is anticipated that expansion or extrusion systems would react similarly. In the latter case, the temperatures are sufficient for the formation of resistant starch, which is a function of amylose content and would presumably be less with the waxy starch type. In the model pellet system waxy barleys provided significantly harder pellets than normal starch barley at a range of temperatures and added moisture levels encountered in feed processing. Whether or not this can be attained commercially remains to be determined. In related studies (Ankrah, 1994) normal starch hull-less barley resulted in pellets that were significantly harder than pellets from corn (p< 0.01) and not significantly different than pellets from wheat. Corn starch also had a higher gelatinization temperature range (62±728C) than barley (51±608C) or wheat (56±648C) starches (Biliaderis, 1980).
The totalb-glucan content is consistently and significantly higher in waxy hull-less barley than in normal isotype (Ullrich et al., 1986; Xue et al., 1991). In the present study, the high extract viscosity associated with hull-less barley (without b-glucanase) was evident in both the PSI and DSI. Waxy barley in general had higher extract viscosity than the normal hull-less barley in the absence of enzyme supplementation, and pelleting alone tended to reduce viscosity. This latter effect may be due to a shearing effect on
b-glucan during pelleting, or, more likely, the pelleting procedure that was used provided some opportunity for b-glucan degradation due to endogenous b-glucanase during the conditioning process, which allowed a longer period of exposure than normal pelleting. Clearly, however, the dominant effect in terms of intestinal viscosity reduction was
b-glucanase supplementation, which greatly reduced viscosity levels. As observed previously with high and low viscosity barleys (Campbell et al., 1989, Campbell et al., 1993), there were no differences among barleys attributable to viscosity differences when supplemented with dietary enzymes.
Extract viscosity provides a uniform measure of intestinal viscosity, however, it is reasonable to expect that in vivo there is a concentration gradient with viscosity increasing with proximity to the cell surface, reflecting gradual dissolution of the cell wall during digestion. The similarity in extract viscosity between the proximal and distal small intestine indicate that this process was virtually complete in the proximal region. High b-glucan induced viscosity has a pronounced effect on digestibility of most nutrients, but especially fat (Campbell and Bedford, 1992). Starch digestion is affected as well, but in this case the effect was to shift starch digestion posteriorly, rather than affect total digestibility. In the present study, overall starch digestibility was reduced as well in the case of the normal starch hull-less barley without enzyme supplementation. The granule surfaces of raw waxy starch are covered with natural fissures, which, along with
higher solubility of amylopectin, has been suggested to enhance susceptibility to a -amylase. There was no indication of higher starch digestion in the PSI with waxy starch type in enzyme-supplemented, non-pelleted diet compared to the normal starch type, indicating that any granular surface differences had no effect. The effect of heat on starch digestion can also be explained in terms of partial granule disruption increasing the rate of degradation bya-amylase. The effect of heat treatment imparted by the conditioning/ pelleting process on starch digestion was most apparent in the proximal small intestine, where starch digestion was considerably greater in the pelleted as opposed to the untreated hull-less barley, in the absence of dietary enzyme. The waxy hull-less barley was numerically, but not statistically higher in starch digestion than the normal hull-less barley in the pelleted feed supplemented with enzyme. The most consistent factor affecting starch digestion was the inclusion of dietary b-glucanase, followed by heat treatment and finally, starch type. Waxy starch only offered an apparent advantage in the enzyme-supplemented, pelleted diets which may relate to its lower gelatinization temperature.
While starch digestion in poultry is virtually complete, Hesselman and Aman (1986) considered starch digestion in the lower regions of the small intestine as less efficient than anterior regions because of the presence of indigenous microflora, which compete with the host for digested products. Greater starch digestion in the proximal small intestine, whether accomplished by enzyme supplementation, heat processing, or starch type differences, may be interpreted as a higher rate of starch digestion, which introduces other potential metabolic savings. Nutrient assimilation may be higher within a given time period, which would ultimately be reflected in higher feed consumption, and faster growth. Anterior digestion of starch may also be indicative of reduced enzyme protein required to digest starch, protein which could then be channeled for growth and development. Heat and moisture treatment as it occurs during pelleting may obliterate differences in starch digestibility attributable to granular surfaces.
Chick performance, as reflected by body weight gain, feed intake, and feed conversion, did tend to correspond to starch digestibility in the proximal small intestine. As observed previously, with waxy and normal starch barley, starch type influenced body weight gain and feed efficiency (Newman and Newman, 1987). The major response was to enzyme addition, where body weight gain improvement approached 50%. Among the enzyme supplemented groups there were no significant differences attributable to heat treatment (pelleting) or starch type, indicating that the digestibility differences attributable to these factors were insufficient to affect performance parameters, or the response magnitude was below detectable levels under the conditions of the assay.
It may be concluded from this study that high amylopectin hull-less barley may offer advantages in feed processing associated with its lower gelatinization temperature. The higherb-glucan affiliated with the waxy trait would seriously confound the analysis of nutritional value in diets which did not include an enzyme supplement. Although experimental results have indicated that the effect due to highb-glucan is not a major concern in enzyme-supplemented diets (Campbell et al., 1989, Campbell et al., 1993), barley breeders should strive to lowerb-glucan genetically to at least moderate levels if waxy starch-type barleys are developed for feed applications.
References
Ankrah, 1994. Heat and moisture effects on the nutritional and physical characteristics of starch in normal and waxy hull-less barley. M. Sc. Thesis. University of Saskatchewan.
Association of Official Analytical Chemists, 1990. Official method of analysis, fifteenth ed., pp. 152±169. Biliaderis, 1980. Physiochemical studies on legume starches. Ph.D. thesis. University of Saskatchewan. Bjorck, I., Nyman, M., Pederson, B., Siljesstromm, M., Asp, N-G., Eggum, B.O., 1987. Formation of enzyme
resistant starch during autoclaving of wheat starch: studies in vitro and in vivo. J. Cereal Sci. 6, 159±172. Campbell, G.L., Bedford, M.R., 1992. Enzyme applications for monogastric feed: a review. Can J. Anim. Sci.
72, 449±466.
Campbell, G.L., Rossnagel, B.G., Bhatty, R.S., 1993. Evaluation of hull-less barley genotypes varying in extract viscosity in broiler chick diets. Anim. Feed Sci. Technol. 41, 191±197.
Campbell, G.L., Rossnagel, B.G., Classen, H.L., Thacker, P.A., 1989. Genotypic and environmental differences in extract viscosity of barley and its relationship to its nutritive value for broiler chickens. Anim. Feed Sci. Technol. 26, 221±230.
DeHaas, B.W., Goering, K., 1972. Chemical structure of barley starches. 1. A study of the properties of the amylose and amylopectin from barley starches showing a wide variation in Brabender viscosity curves. Starke 24, 145±149.
Fenton, T.W., Fenton, M., 1979. An improved procedure for the determination of chromic oxide in feed and feces. Can. J. Anim. Sci. 59, 631±634.
Goering, K., Eslick, R., DeHaas, B.W., 1973. Barley Starch. V. Comparison of the properties of waxy compana barley starch with the starches of its parents. Cereal Chem. 50, 322.
Hesselman, K., Aman, P., 1986. The effect ofb-glucanase on the utilization of starch and nitrogen by broiler chickens fed barley of low or high viscosity. Anim. Feed Sci. Technol. 15, 83±93.
Newman, R.K., Newman, C.W., 1987. Beta-glucanase effect on the performance of broiler chicks fed covered and hulless barley isotypes having normal and waxy starch. Nutr. Rep. Int. 36, 693±697.
Salih, M.E., Classen, H.L., Campbell, G.L., 1991. Response of chicken fed on hull-less barley dietaryb -glucanase at different ages. Anim. Feed Sci. Technol. 33, 139±149.
SAS, 1989. SAS Institute, Box 8000, Cary, NC, USA 27512-8000.
Schoch, 1969. Mechano-chemistry of starch. Wallerstan Lab. Commun. 32, 149±159.
Thomas, M., Van der Poel, A.F.B., 1996. Physical quality of pelleted animal feed. 1. Criteria for pellet quality. Anim. Feed Sci. Technol. 61, 89±112.
Ullrich, S.E., Clancy, J.A., Eslick, R.F., Lance, R., 1986.b-glucan content and viscosity of extract from barley. J. Cereal Sc. 4, 279±285.
Xue, Q., Newman, R.K., Newman, C.W., 1991. Waxy gene effects onb-glucan, dietary fiber content, and viscosity of barleys. Cereal Res. Comm. 19, 339±404.
Zobel, H.F., 1984. Gelatinization of starch and mechanical properties of starch pastes. In: Whistler, R.L., Pascall, E.F. (Eds.), Starch: Chemistry and Technology, second ed., Academic Press Inc. Orlando, pp. 285±309.
