Studies On Fermentation Technology Of Fermented Mulberry Beverage And Effects Of High Hydrostatic Pressure Treatment On Its Quality

The study explored fermentation of mulberry beverage using mixed cultures of yeast and lactic acid bacteria. The fermentation conditions were optimized by single factor test and response surface methodology. In addition, the fermented mulberry beverage was sterilized using high hydrostatic pressure(HHP) considering the heat sensitivity nature of mulberry. The effect of different HHP conditions on fermented mulberry beverage quality was studied, which provided theoretical and experimental basis for application of HHP technology in sterilization mulberry beverage. The main research contents and conclusions are as follows:(1) The optimal fermentation parameters were obtained using sensory evaluation as an indicator. Based on the indicator, the product was firstly fermented using yeast followed by the addition of Lactobacillus to serve as mixed fermentation. During the fermentation, 71 B yeast and Lactobacillus plantarum were selected. The optimum fermentation conditions for 71 B yeast were: inoculum concentration of 5.8% at a temperature of 27 ℃ and fermentation time of 7.5 h, while those for the Lactobacillus plantarum were 0.25% inoculum concentration, temperature of 36 ℃ and fermentation time of 22.5 h.(2)The fermented mulberry beverage was sterilized by HHP and the results are as follows:there was no significant change(p<0.05) in soluble solids; p H value significantly decreased(p<0.05) while total acid contents increased significantly(p<0.05) The results also revealed no significant change(p>0.05) in polyphenol and anthocyanin contents but a significant(p<0.05) increase in the total flavonoid content.(3)CIEL*a*b* parameters of HHP sterilized fermented mulberry beverage were determined and compared with those of untreated samples. Significant change(p<0.05) was observed in brightness(L*) and red hue(a*) while no significant change(p>0.05) was observed in yellow hue(b*). Moreover, the color differences(ΔE) between treated and untreated samples were less than 2.0, indicating that HHP treatment had no significant effect on the color of fermented mulberry beverage.(4)Amino acid automatic analyzer was used to study the effect of HHP on free amino acids of fermented mulberry beverage. It was found that HHP treatment had no significant effect on the free amino acids profile, however, the contents of free amino acids of treated samples were significantly higher(p<0.05) than those of the untreated samples. The proportions of bitter amino acids in treated samples were basically the same as untreated samples. However, an increase in proportion of sour amino acids and a decrease in the proportion of sweet and astringent amino acids were observed.(5)Nine organic acids: oxalic acid, tartaric acid, pyruvic acid, 2-keto-glutaric acid, lactic acid, acetic acid, citric acid and succinic acid were detected in the fermented mulberry beverage using RP-HPLC. HHP treatment had no effect on the organic acids profile in fermented mulberry beverage but on their contents(p<0.05). The study also revealed that at a constant dwell time, the contents of the organic acids increased as the pressure increased. However at a constant pressure, the organic acid contents of the treated samples firstly increased and then declined as dwell time increased with the highest organic acid contents at a dwell time of 15 min.(6)The effect of HHP treatment on the aroma compounds in fermented mulberry beverage was analyzed by headspace solid phase micro extraction(HS-SPME) and gas chromatography-mass spectrometry(GC-MS). It was found that the contents of alcohols and acids declined as the pressure increased, but the contents of esters increased compared to those of the untreated samples. As the dwell time increased, the alcohols and acids contents in the fermented mulberry beverage reduced while esters contents increased and subsequently decreased. The optimal production conditions at which the aromatic components of the fermented mulberry beverage could be improved are at a pressure of 400 MPa and a time of 15 mins. This was consistent with sensory evaluation results.