| Mulberry vinegar is made by alcoholic and acetic acid fermentation of mulberry juice. It has the nutritional and functional properties of both mulberry and vinegar. In addition the healthy fruit vinegar has a unique flavor and color. The production of the healthy fruit vinegar has some constrains such as suitable raw material selection, limited research on acetic acid fermentation and long aging time. So a method for screening the mulberry varieties were established and the suitable mulberry varieties were identified. The acid production rule during acetic acid fermentation was studied and the fermentation parameters were optimized. The effect of High Hydrostatic Pressure(HHP) on mulberry vinegar were studied and the function of HHP on aging were identified. The study provides a theoretical basic for processing and production of mulberry vinegar. The main work and conclusions are as follows:(1) In order to select the suitable mulberry varieties for vinegar prodcution, the database of p H, soluble solids concentration, total sugar content, total acid content, sugar-acid ratio, total polyphenols content, total anthocyanins content, chromatic properties, free amino acid of nine mulberry varieties include ziyahusang, dashi, zhen8603, zhen8607, zhen9106, zhenshen1, hongguo2, sheyang5, huaichang20 was built. A mulberry variety screening method was established through Principle Component Analysis(PCA) combined with sensory evaluation. Zhen1, hongguo2 and dashi were selected as suitable varieties for mulberry vinegar production using the screening method.(2) Using the total acid production and sensory evaluation results as main indicators, the suitable acetic acid bacterium was screened from zhongke AS1.41, huniang 1.01 and LB acetic acid bacteria. The results showed that a LB acetic bacterium was the most suitable one. A second order polynomial equation for the acetic acid fermentation craft of mulberry vinegar was established with response surface methodology based on the total acid content. The data indicated that the optimum acetic acid fermentation parameters of the mulberry vinegar were: inoculum concentration of 10.63%, fermentation temperature of 31 oC, initial alcohol content of 5.88%, and liquid volume of 18.25%. The obtained maximum acidity was 5.58 g/100 m L.(3) Headspace Solid-Phase Micro-Extraction(HS-SPME) coupled with Gas Chromatography-Mass Spectrometry(GC-MS) techniques was used to analyze aroma components in mulbrry vinegar. From the results, forty aroma components: esters(20), alcohols(11), acids(4), aldehydes(2) and ketones(3) were identified in mulberry vinegar. Characteristic aroma components of mulberry vinegar were ethyl acetate, isobutyl acetate, ethyl butyrate, isoamyl acetate, ethyl caproate, ethyl caprylate, phenethyl acetate, iso-amyl alcohol, phenethyl alcohol, acetic acid, nonanal, benzaldehyde and 2-butanone. The aroma components were mainly fruity, floral, ester, sweet fruit and vinegar aroma which constituted the unique aroma of the mulberry vinegar.(4)After treated by HHP, the total content of volatile esters were significantly increased and the total content of volatile alcohols and acids were significantly reduced(p<0.05), so the aging fuction of HHP was idenntified. Meanwhile there was no significant effect on total sugar content and chromatic properties of mulberry vinegar(p>0.05). HHP treatment at 200 Mpa for 15 min brought no significant effect on total acid, total polyphenols and total anthocyanins contents of mulberry vinegar(p>0.05). However, HHP treatment at 300 Mpa and above for 15 min or HHP treatment for 15 min and above, significantly reduced the total acid, total polyphenols and total anthocyanins contents of the mulberry vinegar(p<0.05). There was no significant effect on the reduction of total polyphenols and total anthocyanins contents of the mulberry vinegar treated by HHP(p>0.05), respectively 2.50%~4.10% and 3.59%~6.02%.(5) PCA was used to divide the mulberry vinegar treated by different HHP into four categories based on the different aromatic components. Mulberry vinegar treated at 200 MPa for 15 min, 300 MPa for 15 min, 400 MPa for 15 min and 400 MPa for 25 min were in the same category. Mulberry vinegar at 400 MPa for 20 min and 500 MPa for 15 min were also in the same category while Mulberry vinegar treated at 400 MPa for 10 min and non-HHP treated vinegars were in different categories. The aroma components which highlighted the differences in mulberry vinegar treated with different HHP were identified... |
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