HUSEIN, Ibrahim Aldaw Ibrahim (2020) Development of Cow-Goats Yoghurt Powder (CGYP) by Optimization on Fermentation Conditions and Drying Methods. Doctoral thesis, Universitas Jenderal Soedirman.

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Abstract

This research is aimed to treat fresh cow-goats milk with a heating process to provide optimal pasteurization conditions that do not influence the cow-goats milk chemical composition to suite production of yogurt from combination between cow-goats milk. In addition, to assess and find the best method of dehydration cow-goat yogurt to longer the shelf life of it. The pasteurization conditions considered were: temperature (72, 80 and 85oC), and time (5, 10, and 15sec); the combination between cow-goats milk were: (00:100, 25:75, 50:50, 75:25, and 100:00 (v/v) respectively; incubation conditions considered were: temperature (40, 43, and 46oC) and LAB concentration (5, 10, and 15%); the dehydration methods were: method (freeze-dryer) at time (16, 19, and 22hr) and spray-dryer (inlet temperature 160˚C, outlet temperature 80-90˚C and feeding temperature at 15˚C); the rehydration of cow-goat yogurt powder were: water temperature (40˚C), time of rehydration for (30 minutes), water ratio to powder yogurt were: (1:3, 1:4, and 1:5); yogurt powder samples were packaged in aluminum foil and storage at room temperature for six months; tow-way ANOVA and t-test were performed to evaluate the difference between data by Microsoft Excel Version 13, and separate between means used Multiple Duncan Test. These results of heat treatment shown there were a significant difference (P<0.05) between treated milk and SNI (Standards National Indonesia) on viscosity and pH; whereas was no significant differences in density and titratable acidity. And results of incubation conditions showed there were a significant difference (P<0.05) between all cow-goat yogurt samples in amount of lactic acid bacteria, total solids, pH and viscosity; whereas were no significant differences in density, titratable acidity and color. The results of dehydration yogurt by freeze-dryer shown there was a slightly significant effect on compositions of cow-goat yogurt powder, whilst no significant differences on number of bacteria cells, in the other side spray-dryer had a negative significant on chemical compositions and deceased the total lactic acid bacteria cells. The general results of these study the heat processing concluded the temperature and time had a significant effect on nutritional compounds of goat milk, with an increase in lactose and non-fat solids contents; therefore, treated goat milk at 85oC to 5sec is best than other treatments. The results of pasteurization temperature and time had a significant effect on decreased the protein, fat, viscosity and pH of mixed cow-goats milk, with an increased in lactose, total solids and non-fat solids of combination of cow-goats milk; moreover, heated mixed cow-goats milk at 85oC to 15s is the best in improving the functional quality of mixed cow-goats milk, thus, it suitable to produce cow-goat milk yogurt. The results of incubation condition proved the ideal state of incubation of cow-goats milk fermentation were: temperature 46oC, culture concentration 10% for 8hr, which was gave the better physicochemical and sensory properties of cow-goat yogurt; whereas the drying yogurt by freeze-dryer for 19hr is an excellent method to preserve the desirable microbiological properties in yogurt and improving quality of final product to comparable to spray-dryer method; while the rehydration yogurt powder to water ratio 1:3 by freeze-dryer gave generally best quality compared to traditional yogurt. The cow-goat yogurt powder had saving its chemical and microbial stability during storage period for six months. Keywords: Cow-Goats Milk; Pasteurization; Incubation Conditions; Dehydration; Rehydration; Physicochemical; Sensory Evaluation.

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