4. RESULTS AND DISCUSSION
4.4 Quality Attributes
4.4.4 Rehydration
Ready-to-eat (RTE) meat products are commonly not evaluated using rehydration as a quality parameter. It is important to note, however, that rehydration rates have a direct bearing on the palatability of these products since they must be masticated and mixed with saliva to soften them before swallowing.
The rehydration characteristic curves for samples of different thickness marinated for 6 hours and dried under the convective air dryer are shown in Figure 4.23. These curves are typical of samples of other marinating durations that were dried under the same conditions (see appendix I). It can be seen that for the samples that were dried under the convective air dryer, 5 mm thick biltong slices rehydrated better than the 10 and 15 mm thick slices while the 15 mm thick slices had the slowest rehydration rates for all thicknesses. The rehydration rises from zero to reach 8.47% after two minutes for 5 mm thick slices, and gradually increases with increasing rehydration time to reach 11.84% after the 10 minutes (Figure 4.23). It can also be observed in that samples of 10 and 15 mm thickness followed a similar trend, although their rehydration rates were lower than that of 5 mm thick slices, with the 15 mm thick slices having the slowest rehydration rates. Samples that had been marinated for different durations showed comparable rehydration characteristics (Appendix I).
Figure 4.24 shows rehydration characteristics of 5 mm thick biltong slices that were marinated for different durations then, dried under the convective air dryer. It can be observed that the 5 mm thick, 24-hour marinated samples’ rehydration rises rapidly from zero
104 to reach 7.29% in a minute. Thereafter, rehydration gradually increased with increasing rehydration time to reach 12.16% in 10 minutes (Figure 4.24). It can also be deduced that the 5 mm thick, 6- and 12- hour marinated samples followed a similar trend, although their rehydration rates were lower than those of 5 mm thick, 12- and 24-hour marinated slices, with the 5 mm thick, 12-hour marinated slices having the slowest rehydration rates. Sample thickness had a more pronounced effect on rehydration than the marinating duration (Figures 4.23 and 4.24)
Figure 4.23 Changes in rehydration with time, when the marinating duration is varied, for 5 mm thick, convective air dried samples
Figure 4.25 presents the rehydration characteristics of samples of different thicknesses previously marinated for six hours then dried under the HWL infrared heater. These curves are typical shape of rehydration curves of 12- and 24-hour marinated that were dried under the same conditions using the HWL infrared heater (see Appendix I). It can be observed in (see Figure 4.25) that the rehydration of 5 mm thick slices rises from zero to 5.36% within a minute, and gradually increases with increasing rehydration time. After 10 minutes of rehydration, it had risen to 12.59%. It is also that samples of 10 and 15 mm thickness followed a similar trend, although their rehydration rates were lower than that of 5 mm thick slices, with the 15 mm thick slices having the slowest rehydration rates for all thicknesses
0 2 4 6 8 10 12 14
0 2 4 6 8 10
Rehydration (%)
Rehydration time (minutes)
5 mm 6 hour 5 mm 12 hour 5 mm 24 hour
105 regardless of the marinating duration for samples that were dried under the HWL infrared heater. Similarly, samples that had been marinated for different durations and dried under the HWL infrared heater showed similar rehydration characteristics to those that were dried under the convective air dryer.
Figure 4.24 Changes in rehydration as a function of time, when the slice thickness is varied, for the 6-hour marinated, high wavelength (HWL) infrared dried samples
Figure 4.26 shows the rehydration characteristics of 5 mm thick samples that were marinated for different durations, then dried under the HWL infrared heater. It can be observed form that the rehydration for the 5 mm, 6-hour marinated biltong slices rises from zero to 5.36%
after a minute, and gradually increases with increasing rehydration time. After 10 minutes, its rehydration was 12.59%.
It can be also be deduced that the 5 mm thick,12- and 24-hour marinated samples followed a similar trend, although their rehydration rates were lower than that of the 6-hour marinated slices, with the 5 mm 24-hour marinated slices having the slowest rehydration rates for all marinating durations (Figure 4.26). The product thickness had a more pronounced effect on rehydration than marinating duration (Figures 4.25 and 4.26).
0 2 4 6 8 10 12 14
0 2 4 6 8 10
% Rehydration
Rehydration time (minutes)
5 mm10 mm 15 mm
106 Figure 4.25 Changes in rehydration as a function of time, when the marinating duration is
varied, for the 5 mm thick, high wavelength (HWL) infrared dried samples Figure 4.27 presents the rehydration behaviour for samples of various thicknesses that were marinated for 24 hours, then dried under the LWL infrared heater. These rehydration curves are the typical shape of rehydration curves of samples of various thickness that were dried under the same conditions after marinating for 6 and 12 hours (see Appendix I). It can be deduced that the 5 mm thick slices rehydrated from zero to 3.37% after a minute, and gradually increased with increasing rehydration time. After 10 minutes, its rehydration was 9.44%.
It can also be observed that samples of 10 and 15 mm thickness followed a similar trend although their rehydration rates were lower than that of 5 mm thick slices with the 15 mm thick slices having the slowest rehydration rates for all thicknesses, for samples that were dried under the LWL infrared heater (Figure 4.27). Samples that were marinated for different durations showed similar behaviour to the rehydration characteristics of samples that were marinated for 24 hours, depicted in Figure 4.27 (see Appendix I).
0 2 4 6 8 10 12 14
0 2 4 6 8 10
Rehydration (%)
Rehydration time (minutes)
5 mm 6 hour 5 mm 12 hour 5 mm 24 hour
107 Figure 4.26 Changes in rehydration as a function of time, when the slice thickness is varied,
for the 24-hour marinated, low wavelength (LWL) infrared dried samples
Figure 4.28 presents rehydration characteristics of 10 mm thick biltong slices that were marinated for 6, 12 and 24 hours then dried under the LWL infrared heater. It can be observed that the 10 mm, 6-hour marinated biltong slices rehydration rose from zero and reached 4.25% in a minute, and then gradually increased with increasing rehydration time (Figure 4.28). After 10 minutes, its rehydration was 12.57%. It can be also be clearly seen that the 10 mm thick samples that were marinated for 12 and 24 hours followed a similar trend, although their rehydration rates were generally lower than those marinated for 6 hours, with the 24-hour marinated slices having the slowest rehydration rates for all marinating durations. It can also be observed from the rehydration curves in Figure 4.27 and Figure 4.28 that the differences in rehydration rates due to product thicknesses appear to be comparable to differences in rehydration due different marinating durations. It can be conclude that the 6- hour marinated slices (see Figure 4.28), had better rehydration characteristics compared to those of 12- and 24-hour marinated biltong slices.
Samples dried under the three drying systems showed that the HWL infrared heater had better rehydration characteristics than those dried under the LWL heater and the convective air dryer. In addition, 5 mm thick biltong slices had higher rehydration rates than 10 and 15 mm
0 1 2 3 4 5 6 7 8 9 10
0 2 4 6 8 10
% Rehydration
Time (minutes)
5 mm10 mm 15 mm
108 thick samples. However, marinating duration had varied effects on biltong products dried under each of the three drying systems assayed. Samples that were marinated for 24 hours, had higher rehydration rates than those marinated for 6 and 12 hours for biltong slices that were dried under convective air drying system. On the other hand, samples marinated for 6 hours had higher rehydration rates compared to those that were marinated for 12 and 24 hours for biltong slices that were dried under the HWL and LWL infrared heaters.
Figure 4.27 Changes in rehydration as a function of time, when the marinating duration is varied, for the 10 mm thick, low wavelength (LWL) infrared dried samples It was observed that when samples were rehydrated for durations longer than 10 minutes, there was an increase in their rehydration. It is expected that, with an increase in rehydration time beyond 10 minutes, there will be a gradual increase in rehydration to a point where rehydration will no longer increase with increasing rehydration time.
A three-way ANOVA was carried out on the mean rehydration values for the samples in order to investigate the effects of product thickness, marinating time and the drying system on the rehydration characteristics of biltong. Both the drying system used to dry the samples and the marinating time had no significant (p0.05) effect on the average rehydration rates of biltong slices. There was however significant (p0.05) differences between the average rehydration rates for dry samples of different thicknesses. The average rehydration rates
0 2 4 6 8 10 12 14
0 2 4 6 8 10
Rehydration (%)
Rehydration time (minutes)
10 mm 6 hour 10 mm 12 hour 10 mm 24 hour
109 between samples of all thicknesses were significantly different. The interaction between the drying system and the product thickness or the marinating duration, as well as between the product thickness and the marinating duration was not statistically significant (p0.05) for product rehydration. The three-way interaction between the drying system, product thickness and the marinating duration was also statistically not significant (p0.05).
In summary, the sample thicknesses had a significant effect on the rehydration rates of biltong while the drying system used as well as different the marinating durations assayed, gave comparable rehydration behaviour of biltong products. The rehydration values in this study were, however, low compared to those reported in studies by Nathakaranakule et al.
(2007) that ranged from 57.17% to 86.66%. Differences in rehydration rates between their study and the present study may be attributed to differences in the drying method used and the inherent biological constitution of the products under investigation. In their study, they rehydrated chicken meat that was dried using superheated steam and heat pump-assisted superheated steam, and this implies a product of lower fibre density compared to that of beef, and a drying system that operated at higher temperatures (above 100oC) compared to those of the present study.
4.4.5 Microbiological safety