Study On The Coconut Yogurt Making And Quality Analysis

Coconut is mainly produced and processed in Hainan,China,with coconut milk,coconut candy,coconut powder and coconut oil being the primary processed products.In order to develop new product and increase the additional value,we conducted systematic studies on the ingredients,fermentation strains and fermentation conditions using coconut milk as the primary raw material to obtain coconut yogurt products with a tropical flavour.In addition,the quality changes of coconut yogurt before and after fermentation were analysed using HPLC,GC and GC-MS,and the primary aroma characteristics of coconut yogurt were determined.The quality changes of coconut yogurt during storage were analysed using a texture analyser,an electronic nose and an electronic tongue,and the best edible period of coconut yogurt was determined.The major conclusions are as follows.(1)Study on coconut yogurt ingredientsThe effects of the addition of coconut milk,emulsifier,thickener and sucrose on the overall quality of coconut yogurt were analysed through a single-factor experiment,and the most suitable ingredient formation was follows.30%coconut milk,7%sucrose,0.8%gelatin,0.3%hydroxypropyl distarch phosphate,0.3%pectin 0.02%emulsifiers(sucrose ester-11 and monoglyceride were 0.005%and 0.015%,respectively),and 2%whey protein and sodium caseinate(1:1).(2)Effects of strains and fermentation conditions on coconut yogurtThe effects of Streptococcus thermophilus,Lactobacillus bulgaricus,L.plantarum and L.casei and mixed strains on the overall quality of coconut yogurt were analysed.The best-quality coconut yogurt was obtained by the mixed fermentation of S.thermophilus,L.bulgaricus,L.casei and L.plantarum(1:1:1:1).Meanwhile,the effects of inoculum and fermentation temperature on the quality of coconut acid were also investigated.The optimum inoculation amount of coconut yogurt was 3%,and the optimum fermentation temperature was 42 ?.(3)Changes of sensory quality of coconut yogurt before and after fermentationSolid-phase microtraction(SPME)combined with gas chromatography-mass spectrometry(GC-MS)was used to analyse the flavour compounds of set-type coconut yogurt.The organic acids and fatty acids were analysed by high-performance liquid chromatography and gas chromatography,respectively.2,3-butanediol,acetic acid,L-lactic acid,caprylic acid,3-hydroxy-2-butanone and tert-octanolactone were identified as the primary characteristic flavour components of coconut yogurt,and the major aroma characteristics of coconut yogurt were coconut,milky and light sour.3-hydroxy-2-butanone,D-limonene and decene were found as newly produced substances during the fermentation.It was determined that lactic acid,oxalic acid,succinic acid and fumaric acid were the primary organic acids in coconut yogurt.Methyl octanoate,methyl decanoate,methyl laurate,methyl myristate,methyl palmitate and methyl stearate were the primary fatty acid esters of coconut yogurt.The levels of the beneficial components of methyl laurate,methyl myristate and methyl palmitate increased by lactic acid fermentation.(4)Quality changes of coconut yogurt during storageThe quality changes of coconut yogurt during storage were analysed using physical and chemical analysis,texture analysis and sensory analysis.With the prolongation of storage time,the sugar content,the pH and the viable count of coconut yogurt gradually decreased,whereas the acidity and the water-holding capacity gradually increased.The values of hardness and elasticity of coconut yogurt gradually decreased,whereas the values of viscosity and cohesion gradually increased.Analysis of changes in aroma and taste of coconut yogurt during storage using the electronic nose and the electronic tongue showed no significant differences in aroma and taste of coconut yogurt during the first 21 days of storage;however,there was a significant change in the aroma and taste of coconut yogurt stored for 28 days.Therefore,coconut yogurt can be consumed within the first 21 days to maintain its high eating quality.