Advances in Food Science and Engineering

6

Authors: P. R. Davara, N. C. Thumar, J. J. Limbasiya, H. V. Agravat, V. P. Sangani

Wheat is the most important mainly due to its use in the flour production. An experiment was conducted to study the feasibility of evaporative water cooled grinding for wheat flour production. Wheat was mixed with water (0%, 3%, 6% and 9% w/w) and grinded immediately using domestic hammer mill before the surface water penetrated into the grain. The different grinding characteristics were studied for the grinding operation. This process resulted in cooling since the evaporating particles carried away the heat generated inside the grinding mill resulting in decrease of the temperature of the system. The temperature during grinding was found to be decreased by 11°C under for the sample wetted with 9% (w/w) of water as compared to conventional grinding. No sieve clogging was observed during evaporative water cooled grinding. Grinding time was observed to be increased by 155 sec for the evaporative water cooled ground sample. This study revealed that the evaporative water cooled grinding method can be effectively used for avoiding the rise in temperature during grinding in order to preserve the quality of wheat.

8

Authors: Olusegun A. Olaoye, Stella C. Ubbor, Iniobong G. Lawrence

This study examined the effect of different packaging materials on some quality indices of a Nigerian stick meat (tsire) during spontaneous storage at 30oC for four days. The packaging materials included those normally used for wrapping of the product during sales to consumers, and they were ‘common paper’, ‘dry banana leaves’, ‘cellophane paper’ and ‘aluminium paper’. Analysis during storage showed that the tsire samples stored in cellophane paper had the highest concentration of lactic acid (14g/kg), while 10g/kg was recorded as the lowest concentration for samples stored in common paper. There was reduction in pH of the tsire samples stored in the different packaging materials during storage from 6.9 on day 1 to 5.9 on day 4, although no significant difference (p>0.05) was recorded between samples. Thiobarbituric acid (TBA; mg malonaldehyde/kg sample) ranged from 0.38 and 040 on day 1 among the different samples, and the values increased during storage to a range of 0.74 to 0.81 on day 4; however, the values did not differ significantly (p>0.05) among samples. Principal component analysis (PCA) of the volatiles associated with the tsire samples during storage indicated that known spoilage compounds, including nonanal and heptanal, were detected in all samples, especially on days 3 and 4. In conclusion, the different packaging materials recorded no significant effect (p>0.05) on the tsire samples during storage. However, TBA values and volatiles recorded suggested likely presence of spoilage in the samples during storage.

10

Authors: Fernanda Rosa Assis, Rui Manuel Santos Costa de Morais, Alcina Maria Miranda Bernardo de Morais

The effects of the pre-osmotic treatment on the mass transfer kinetics of the freeze-drying (FD) and on the water activity (aw) and the quality – colour, total phenolic content, antioxidant activity – of apple cubes were studied. The fit of the moisture content was carried out using several mathematical models. The comparison among FD, microwave drying (MWD) and hot air drying (HAD) of osmotically treated apple cubes was also performed according to the drying rate and the aw. The apple cubes were osmotically treated with 60ºBrix sucrose or sorbitol solutions at 60ºC, then frozen and freeze-dried. The FD reduced significantly the moisture content from 6.259, 1.086 and 1.031 to 0.138, 0.099 and 0.074 kgwater.kgdry matter-1 for the control and the samples osmotically pre-treated with sucrose and sorbitol, respectively. The modified Page’s model presented the highest precision of parameter estimates. The FD of samples osmotically pre-treated with the sucrose solution resulted in a higher drying rate than the others samples. The highest reduction in aw was observed in the fresh samples. After FD, the total phenolic content and the antioxidant activity of the osmotically pre-treated samples decreased around 80%, in comparison with the fresh apple, this reduction being due to the osmotic pre-treatment. The freeze-dried control samples achieved a lower aw in comparison with HAD and MWD. However, FD presented a lower drying rate.