| Lactobacillus is a kind of non-spore,gram-positive bacteria,which main product is lactic acid via metabolism of sugar.Its application range is wide,especially in medicine,food industry.In recent years,lactic acid bacteria fermented fruit and vegetable is popular,due to its products combining the double advantage of probiotics and the fruit and vegetable raw materials.The healthy products were improved flavor and the shelf life were extended without preservatives.Mulberry as medicine edible berries has many health benefits,contain a variety of active ingredients such as anthocyanins,polysaccharide,resveratrol.But mulberries harvest time is short,the furits were succulency and thin skin not easy transportation and storage,fresh fruit serious loss and the prices are high so they were hard to meet the market demand.In order to comply with the market demand and enrich the variety of products.This study had screed high-quality strains for mulberry fermentation and developed new and green mulberry drinks,and the quality changes during the fermentation of mulberry pulp and berry antioxidant,antibacterial properties were analyzed.The main research contents and conclusions are as follows:(1)Screening of fermented mulberry strains.The best plant lactobacillus was obtained by the initial screening,re-screening,strain identification and comparing fermentation performance of mulberry,named NCU137.It has a strong acid resistance and bile salts,tolerance to succus gastricus above p H 2.5 and intestinal environment,high osmotic stress resistance.2%inoculum dose of NCU137 in MRS,the time of delay,logarithmic period and stable time were 2,16,14 h,the viable counts of NCU137 arrived 9.9 Lg(CFU/m L),and the p H was reduced to 3.6 in 32 h.At this stage,OD value is positively correlated with viable count,and can be used for rough detection of colony count.The bacteria have no bacteriostatic effect on pathogenic bacteria,and the main antibacterial metabolites are lactic acid,which may contain trace amount of others except lactic acid,through adjust of lactic acid,heat treatment,catalase and protease action.(2)Optimization of fermentation conditions of mulberry puree.NCU137 has wide applicability and can ferment different kinds of mulberries.Through orthogonal experiment explored NCU137 mulberries fermentation conditions,the best fermentation conditions as follows:10%fructose syrup,quantity of 0.01%,72 h fermentation time,fermentation temperature 32?.The quality of NCU137fermented mulberry beverage conforms to the requirements of GB/T 31121-2014fruit and vegetable juice and beverage standard.Through mulberry,blueberry and raspberry fermentation mixture,a mixed fermented fruit juice beverage with various health benefits was obtained.(3).The changes of number of viable bacteria and nutrient substance involved in metabolism during the fermentation process of mulberry puree.In the 60 h fermentation system,the number of viable bacteria remained very high,and remained 10~9 CFU/m Lin the the end of fermentation,and the p H value of berries was reduced to about 3.31.The consumption of fructose,glucose and sucrose in the whole fermentation system was 36.64,34.40 and 2.78 g/L respectively.The largest increase in organic acids was lactic acid,with an increase of 19.71 g/L.The decrease of free amino acids was 19.12 mg/100g,and cysteine appeared in the fermentation puree.These changes indicate that sugars and amino acids may be involved in other types of metabolic reactions such as TCA cycle and volatile component metabolism and formation in addition to the energy-producing acid.(4)Changes in flavor before and after fermentation.Before fermentation,47kinds of substances were detected,and aldehydes and alcohols formed the framework aroma system of mulberries.After fermentation,50 kinds of substances were detected,and the volatile components of 19 kinds of fresh fruits were retained.The total number of esters decreased but the species increased by 3.The increase in the content of the alkene was significant,especially 9-methyl-1-undecene,and the relative content increased from 7.636%in the fresh puree to 34.584%.The increase of volatile components concentration and species may be come from protein of mulberry or bacteria via lactic acid bacteria fermentation.The protein and amino acids formed to alcohol by enzymes deamination,decarboxylation and degradation.They can also be derived from sugar,through the glycolysis of pyruvate into the TCA cycle and then participate in tranforms of amino acids,transmission of organic acids,formation and evolution of alcohols,esters.(5)Protection of anthocyanin in fermentation process and analysis of anti-oxidation and bacteriostatic properties of mulberry puree.External factors which influence the stability of anthocyanins in the fermentation process is mainly the sterilization temperature and time,followed by light.Sugar and fermentation process have little effect on anthocyanins,suggest that sterilization with 90?and20 min,10%sugar and products avoid light preservation were better for fermented mulberries.In addition,mulberry's anthocyanin has a small loss after sterilization,but its antioxidation and antibacterial properties are obviously enhanced.The antioxidant properties of fermentation puree increased by about 1 times,and the antioxidant capacity was about 6.25 times of V_C and 36 times of V_E.The bacteriostatic ability was similar to that of penicillin sodium 50?100?g/m L.Might be lactic acid bacteria fermentation makes lower p H of puree system,the structure of the anthocyanins more stability contribute to its antioxidant and antibacterial properties.It probably produced substances which have antioxidation and antibacterial properties in the fermentation process of lactic acid bacteria.These substances with resveratrol/anthocyanin increased antioxidant and antibacterial properties.Many data indicate that mulberries via lactic acid bacteria fermentation produced high levels of lactic acid bacteria;enhanced the antioxidant and antibacterial properties;improved taste.The change of mulberries in line with the pursuit of healthy green food for the masses and have the development potential of health drink. |
PDF Full Text Request