Study On Preparation And Storage Quality Of Normal Temperature Brown Yoghurt

Yogurt is favored by consumers because of its good flavor,high nutritional value and regulation of gastrointestinal function.In recent years,with the rapid development of yogurt industry and the swift expansion of market scale,the development of yogurt has been facing problems such as insufficient milk source,high cost of cold chain,short shelf life and insufficient flavor diversification.To address the above problems,a normal-temperature type brown yogurt was prepared in this paper using milk powder as raw material.After browning,the product develops a unique flavour and colour,and after complete fermentation,secondary sterilisation is carried out to inactivate the lactic acid bacteria to obtain ambient yoghurt.In this paper,reducing sugars were screened,the browning,fermentation and sterilisation process conditions were optimised,and changes in the properties of the product at different storage temperatures were investigated.The main contents and results are as follows:1.The color changes of browning reaction between xylose,fructose,glucose and raw milk were investigated.The results showed that when the browning time was 1.5 h,the color value of yoghurt in xylose group,fructose group and glucose group increased by 137.19%,27.03% and 17.28% respectively,and the xylose with the strongest browning reaction was identified as the sugar for this study.The effects of xylose content,browning temperature and browning time on the quality of brown yoghurt were further studied.The optimal browning reaction conditions were determined as follows: 4% xylose content,95 °C browning temperature and 30 min browning time.2.The effects of fermentation temperature,fermentation time,amount of whole milk powder and inoculant amount of fermenting agent on the quality of normal-temperature type brown yogurt were studied.The optimum fermentation conditions were determined as follows: fermentation temperature 43 °C,fermentation time 8 h,inoculant amount 0.1‰ and whole milk powder 11%.3.The effects of sterilization temperature and time on the stability and inactivation of lactic acid bacteria in normal-temperature type brown yoghurt were studied.The optimal sterilization conditions were determined as 75 °C for 15 s,with water holding capacity and total number of lactic acid bacteria as evaluation indexes.The effects of pectin,agar and acetylated starch phosphate on the quality and stability of normal-temperature type brown yoghurt were investigated.The best stabilizer combination was determined by taking water holding capacity,instability index and rheological properties as evaluation indexes.The addition amount of acetylated starch phosphate was 1.5%,and that of pectin and agar was 0.15%.The results showed that after 30 days of storage at 25 °C,37 °C and 47 °C,the color values of the product increased by 13.80%,31.06% and 36.81%,respectively,and there was no significant difference in p H value.Combined with the results of accelerated shelf life experiments,preliminary judgments were made The shelf life of the brown yogurt products prepared in this research can be up to 112 days at room temperature.