Heat Induced Modification Of Whey Protein And Its Applications In Goat Milk Kefir Mild

Goat milk has relatively high nutritional value and low allergy tendency.It's products are getting more and more popular in world.It is difficult to make set type fermented goat milk due to the smaller size of casein micelles and lower content of casein in goat milk.Kefir is an increasingly popular fermented dairy product in the world.However,some defects caused by secondary starter yeast were found in traditional Kefir,which limit the development of traditional Kefir.A new starter culture which called Kefir Mild was available to replace the traditional Kefir.This study aimed to develop set-type and stirred fruit flavored goat milk Kefir Mild using heat induced polymerized whey protein(PWP)as a thickening agent.This study includes into three parts:(1)Optimization of thickening agent level for developing a set type goat milk Kefir Mild with good physical property,sensory score and microstructure;(2)Shelf-life study of the optimized goat milk Kefir Mild.(3)Effect of fruit juice concentrate addition technology on rheological and flavor properties and microstructure of stirred goat milk Kefir Mild.Effects of thickening agent on syneresis,viscosity and texture of goat milk Kefir Mild were studied and compared with cow milk Kefir Mild.The goat milk kefir with 0.3% PWP and 0.2% pectin had similar syneresis(5.44%),viscosity(952.86 m Pa·s)and hardness(112.57g),which were comparable to cow milk sample.Sensory evaluation data(5-point hedonic scale)showed that goat milk Kefir Mild with PWP had a higher score of sensory evaluation than control.Scanning electron micrographs displayed a compact and homogeneous protein network of goat milk kefir with PWP and pectin.The new product contains 13.02 % of total solids,3.50% of protein,and 2.90% of fat.No significant difference in viscosity and hardness was observed between goat milk kefir mild and cow milk kefir mild during the 8-week study(p > 0.05).L.Acidophilus population in both samples remained above 106 cfu g-1 during the first 4 weeks.Sodium dodecyl sulfate PAGE photographs showed limited changes in the protein profile for both samples during storage at 4°C.Stirred fruit flavored goat milk Kefir Mild was made by adding yellow peach,strawberry or blueberry juice concentrate.Effects of addition technology(adding fruit concentrate before or after fermentation)on rheological and flavor properties and microstructure of stirred goat milk Kefir Mild were investigated.Samples with fruit juice concentrate added before fermentation showed particle size ranging from 33.03 to 38.23 ?m,apparent viscosity from 0.166 to 0.198 Pa.s,storage modulus from 15.69 to 20.26 Pa(1 Hz)and loss modulus ranging from 9.25 to 12.39 Pa(1 Hz),which were significantly higher than those of samples added fruit juice concentrate after fermentation.Aroma components and contents were analyzed by Headspace-Solid phase micro-extraction – Gas chromatography – Mass spectrometer(HS-SPME-GC-MS).Aroma contents of samples added with fruit juice concentrate before fermentation were lower than those of samples added after fermentation.Microstructure analysis showed that samples with fruit juice concentrate incorporated before fermentation showed a disrupted protein network.Polymerized whey protein can be used for developing probiotic set-type fermented goat milk.Addition technology of fruit juice concentrate has significant effects on the rheological and flavor properties and microstructure of stirred goat milk Kefir Mild.The results of this study may provide useful information for application of polymerized whey protein in fermented goat milk products.