Studies On Purple Sweet Potato Kefir

In this paper, purple potato and milk were considered as raw materials,selecting Saccharomyces cerevisiae SCY1,which was isolated form fermentedvegetable juice by our research group, and lactic acid bacteria XPL-1,which wasbought form Chr.Hansen,mixed as starter culture to get purple potato kefir. Thefermentation processing,storage stability of purple potato kefir and qualityimprovement of purple potato kefir after different presssure HPM treatment weresubsequently analyzed.The process conditions of kefir were studied.The effects of the amount of purplepotatoes, the amount of sugar, fermentation time, fermentation temperature onpH,titratable acidity, chromaticity,rheological characteristics were studied.Combinedwith sensory evaluation,the optimum technological parameters were: purple potatoes1%, the amount of sugar added8%, fermentation temperature32℃, fermentation time18h.The changes of purple potato kefir during storage at4℃were studied. By theend of12days, for the two kinds of kefir,the pH reach minimum.The purple potatokefir was4.135and the pure kefir was4.19;The itratable acidity reach maximum. Thepurple potato kefir was114~0T and the pure kefir was100~0T.The viable count oflactic bacterial reach maximum. The purple potato kefir was4.5×10~8cfu/ml and thepure kefir was2.7×10~8cfu/ml,but slightly declined after12d.The viable count ofyeast grew from10~3cfu/ml to10~6cfu/ml. Rheological curve show that viscoelasticincreased for two kinds of kefir during the storage process.On the palate, the qualityof purple potato kefir was still good,but the quality of pure kefir storage get worseafter storage12d. Overall, the optimal eating quality was after storage6d.Rheological characteristics,microstructure of purple potato kefir were studiedafter HPM treatment. On the Rheology,for improvement viscoelastic of purple potatokefir, the effect was most obvious after100MPa presssure HPM treatment,thefollowing was50MPa,150MPa; In the microstructure, high pressuremicrofluidization can make the purple potato kefir gel network becomes more dense and uniform distribution of voids.The diameter of voids was about15,4,1,8um after0,50,100,150MPa presssure HPM treatment respectively.