Study On Technology Of Walnut Milk By High Density Fermentation

Walnut milk is one of the representatives of plant protein milk production in China.Walnut milk has good anti-oxidation and anti-aging effects.It is warm in nature and sweet in taste and it is good for stomach and brain.In this paper,walnut was used as the raw material and lactic acid bacteria were used as fermentation strains.A fermented walnut milk beverage with milk white,sweet and sour taste,strong sour taste,fine taste,rich nutrition and health care function were obtained through screening,expanded culture and high density fermentation.Screening and extended culture of lactic acid bacteria:Qualitative experiments and performance studies were carried out to select the lactic acid bacteria with fast start-up fermentation,short fermentation cycle and high acid production to determine the best combination of fermentation bacteria.Single factor experiment and L₉?3⁴?orthogonal experiment were used to optimize the preparation process of walnut milk in Lactobacillus medium.On this basis,single factor and response surface method were used to optimize the nutrient medium and culture conditions of high density Lactobacillus.The results showed that the best combination of Lactobacillus plantarum and Enterococcus Italicus was 7×10⁸ CFU/mL,which was better than other lactic acid bacteria.The optimum parameters of walnut milk preparation were:the ratio of material to liquid was 1:10 g/mL,the time of pulping was 15 min,the water temperature was 65?,the homogenization times were twice,and the number of bacteria and acidity were the best under this condition.Based on the above results,the optimal conditions of Lactobacillus plantarum extended culture were:glucose 3.23%,peptone 3.59%,ascorbic acid 0.12%,triammonium citrate 0.41%,inoculation quantity 8%,culture temperature 34?,pH 6.5,culture time 10 h.The optimum conditions of Enterococcus Italicus extended culture were:3.01%glucose,1.12%yeast extract,0.08%ascorbic acid,0.50%triammonium citrate,8%inoculation quantity,37?culture temperature,pH 6.5 and 10 h culture time.The optimal concentrations of the two strains obtained by the optimal condition test were:the optimal viable number of Enterococcus Italicus was 1.85×10¹00 CFU/mL;The optimal viable number of Lactobacillus plantarum was 2.75×10¹00 CFU/mL.This laid a foundation for the subsequent development of high density fermented walnut milk products.Study on the technology of high density fermentation of walnut milk:High density fermentation technology was mainly to study the fermentation conditions and fermentation methods.The results showed that the best carbon source was whey powder,the best concentration was 60 g/L,the best combination ratio of Lactobacillus plantarum and Enterococcus Italicus was 1:2,the best inoculation quantity was 9%,and the best fermentation temperature was 36?.Under this optimal condition,the maximum number of lactic acid bacteria reached 8.1×10⁹ CFU/mL,and the titrable acidity was 77.3°T.The best way of fed-batch fermentation was to add 4 mL whey powder with concentration of500 g/L to the medium at 5 h and 7 h respectively.Fed batch fermentation can shorten the fermentation cycle.It was a very efficient fermentation operation mode.The aim of high density fermentation of walnut milk was achieved:the highest titrated acid concentration was 80.3°T,the highest density of Lactobacillus was 1.12×10¹⁰ CFU/mL,the acidity of the final metabolite increased by 5.7%.After fermentation and ripening at 4?for 24 h,the degree of lactic acid changed little,the state and taste of walnut were better,and it was not easy to layer.Component analysis and functional study of walnut milk in high density fermentation:Physical and chemical indexes,organic acids,amino acids and sugars were detected in wa-lnut milk,and sensory evaluation was completed.The function of high density fermented walnut milk was studied by the experiments of DPPH,hydroxyl radical and O₂?·radical scavenging.The results showed that the number of viable lactobacillus was 1.08×10¹⁰CFU/mL,pH value and titratable acid were 3.95 and 92.5°T respectively,and protein content was 1.45 g/100g,after 24 h of ripening,which met the requirements of national dairy products.Five kinds of organic acids and six kinds of fermentative sugars were detected in walnut milk after fermentation.The total amino acid content of walnut milk was increased by 0.2916%compared with that of unfermented walnut milk.After walnut milk was fermented in high density and ripened at 4?for 24 h,the stability of walnut milk was significantly improved.Under this condition,we obtained the color of white gray,uniform,uniform tissue state,no particles,fine,sweet and sour taste more suitable for the mouth,sour taste more thick,full taste,with a strong fermented walnut milk unique flavor and aroma of high density fermented walnut milk.Its scavenging effect on DPPH,hydroxyl radical and O₂?·free radical was obvious,and the scavenging effect on hydroxyl radical was the most significant,its scavenging ability was equivalent to VC solution with concentration of 13.63 mg/mL,so the high density fermentation walnut milk has superior antioxidant performance.Therefore,the high density fermented walnut milk prepared in this study was rich in nutriens,easy to absorb,delicate in taste,full in taste and rich in probiotics,and had outstanding antioxidant capacity,which had a broad development and application prospect.