Physiological weight loss

4. IN VITRO AND IN VIVO DISINFECTION AND BIOCONTROL TREATMENTS

5.6 Results and Discussion

5.6.2 Physiological weight loss

The additional initial use of either chlorinated water or anolyte water as a disinfectant to remove some of the previously existing surface pathogens resulted in a lower decay severity. Furthermore, with the action of the hot water treatment to induce fruit resistance, as in the case of combined anolyte water, hot water and B13, no incidence of decay was observed due to the disinfecting action of the anolyte water, the curative action of the hot water and the preventative action of the B13. As mentioned in Section 4.5.2.1, anolyte water is described as having disinfecting properties and the B13 as having preventative properties. The addition of hot water further reduced the onset of decay due to the curative property that it is believed to possess (Ben-Yehoshua et al., 2005). Kim et al. (1991) observed an increase in scoparone in citrus fruit after inoculation with P. digitatum, which further increased after a heat treatment at 36°C for 3 days. The induced concentration of scoparone was sufficient to reduce fungal growth in lemon fruit. This also demonstrated the presence of pathogens to elicit fruit resistance. Lesar (2002) found that a dilution of anolyte water of 1:5 and 1:10 resulted in 100% spore eradication on citrus fruit with an exposure time ranging from 30 to 300 seconds. No visible decay of blue mould was observed on kumquat fruit for all treatments. This could be due to blue mould being more prevalent at cooler temperatures (10C) whereas at room temperatures (25C) green mould develops at a faster rate (Brown, 1994). Schirra et al. (2011) also observed green mould to be the main decay agent in kumquat fruit. Therefore, the results obtained for the development of blue mould on the surface of the kumquat fruit has subsequently been omitted from this section. The results demonstrated that combined pre-packaging treatments proved to be more beneficial in inhibiting decay caused by green mould, compared to individual treatments. In particular the treatments of (1) anolyte water + hot water + B13 and (2) hot water + B13 were most beneficial in preventing decay caused by P. digitatum in kumquat fruit.

disinfectant produced lower PWL’s, compared to fruit treated with chlorinated water as the disinfectant. Anolyte water in combination with hot water led to the lowest PWL of only 55.38% (Day 28). A large increase in the PWL can be observed between Days 14 and 21 and 21 and 28, particularly in the combined treatment of chlorinated water, hot water and biocontrol. The two-way interaction between the treatments and the storage period was found to be significant (P≤0.05) with regard to the PWL. Similarly, Singh and Reddy (2006) observed an increase in the cumulative weight loss of orange fruit with an increase in the storage period. The loss in weight could be attributed to (1) respiration where food reserves are used up and (2) transpiration where moisture is lost via microscopic cracks on the fruit surface (Hong et al., 2007).

Table 5.3 Changes in the physiological weight loss (%) of Penicillium digitatum- inoculated kumquat fruit over a 28-day storage period subjected to different integrated pre-packaging treatments

Treatment Storage Period (Days)

0 7 14 21 28

Chlorinated water 0.00^a 34.72^ef 46.98^hi 60.04^kl 86.17^p

Anolyte water 0.00^a 26.94^cd 37.56^efg 58.16^jkl 77.76^o

Hot water 0.00^a 28.69^cde 42.67^gh 60.69^kl 71.81^mno

Biocontrol (B13) 0.00^a 34.34^ef 58.93^jkl 58.93^jkl 81.14^op Chlorinated water + HWT 0.00^a 18.34^b 31.99^de 57.04^jkl 68.03^m Chlorinated water + B13 0.00^a 21.95^bc 34.86^ef 60.05^kl 73.64^no Chlorinated water + HWT + B13 0.00^a 28.11^cde 37.87^efg 49.48^hij 72.92^mno Anolyte water + HWT 0.00^a 25.91^bcd 25.91^bcd 43.56^ghi 55.38^jk Anolyte water + B13 0.00^a 29.44^cde 29.44^cde 59.96^kl 64.52^lm Anolyte water + HWT + B13 0.00^a 23.7^bc 26.43^cd 47.32^hi 62.33^lm

HWT + B13 0.00^a 28.81^cde 35.85^efg 55.9^jk 64.1^lm

Control 0.00^a 31.67^de 43.07^ghi 53.7^j 70.4^mn

Significance

Treatment (A) **

Storage Period (B) **

AB *

CV (%) 22.0

NS, *, ** Non-significant or significant at P≤0.05 or P≤0.001, respectively. Means within a column followed by the same letter(s) are not significantly different from each other according to Duncan’s Multiple Range Test (P≤0.05), (n=3). CV, Coefficient of variation; HWT, hot water treatment; +,

‘combined with’.

Table 5.4 shows the variation in the PWL values of kumquat fruit inoculated with P.

italicum and subjected to different pre-packaging treatments. Similar trends were observed as in the case of green mould-inoculated fruit, where the PWL of the individual treatments were higher than combined treatments. Treatments that included anolyte water as the disinfectant resulted in lower PWL values than those treatments using chlorinated water. B13 alone resulted in the highest PWL of 77.25%, followed by 73.15% in fruit treated with chlorinated water + hot water + B13. The lowest PWL was observed in fruit treated with the combination of anolyte, hot water and B13 of 54.27%. Chlorinated water combined with hot water also resulted in a low PWL of 55.01% by Day 28. Similar observations of reduced weight loss was found by Hong et al. (2007) and Sen et al.

(2007), which was attributed to melting of the epicuticular wax and sealing of surface cracks.

The two-way interaction between the treatments and the storage period had a slightly lower significance at P≤0.05, compared to the treatment and storage period. The increase in the PWL was highest toward the end of the storage period between Days 21 and 28.

The increase in the weight loss could be attributed to the loss in moisture via the microscopic cracks, which appear on the fruit surface (Hong et al., 2007). The loss in weight can also be attributed to respiration where food reserves are being used up and transpiration where moisture is lost to the external environment. A high ambient temperature and low relative humidity further exacerbates these processes. The combined treatments proved to be better at reducing the PWL of kumquat fruit, compared to individual treatments. Treatments incorporating anolyte water reduced the PWL more than treatments using chlorinated water instead.

Table 5.4 Changes in the physiological weight loss (%) of Penicillium italicum- inoculated kumquat fruit over a 28-day storage period subjected to different integrated pre-packaging treatments

Treatment Storage Period (Days)

0 7 14 21 28

Chlorinated water 0.00^a 21.10^de 34.95^g 46.9^hij 66.05^l

Anolyte water 0.00^a 16.83^cd 29.73^efg 50.42^ij 69.51^lm

Hot water 0.00^a 13.97^bcd 29.56^efg 38.11^gh 68.46^lm

Biocontrol (B13) 0.00^a 16.07^cd 35.73^g 41.3^ghi 77.25^m

Chlorinated water + HWT 0.00^a 9.91^ab 32.03^fg 35.18^g 55.01^ijk Chlorinated water + B13 0.00^a 13.18^bcd 23.05^def 35.04^g 62.10^kl Chlorinated water + HWT + B13 0.00^a 19.29^cde 27.76^ef 44.25^hi 73.15^m Anolyte water + HWT 0.00^a 14.73^bcd 22.35^de 23.32^def 56.95^jk Anolyte water + B13 0.00^a 9.42^ab 19.12^cde 44.07^hi 57.2^jk Anolyte water + HWT + B13 0.00^a 17.24^cd 24.33^def 31.29^efg 54.27^ijk

HWT + B13 0.00^a 10.39^abc 21.35^de 23.22^def 56.48^jk

Control 0.00^a 11.06^bc 33.3^fg 35.36^g 70.07^lm

Significance

Treatment (A) **

Storage Period (B) **

AB *

CV (%) 22.6

NS, *, ** Non-significant or significant at P≤0.05 or P≤0.001, respectively. Means within a column followed by the same letter(s) are not significantly different from each other according to Duncan’s Multiple Range Test (P≤0.05), (n=3). CV, Coefficient of variation; HWT, hot water treatment; +,

‘combined with’.