Influence on the aroma substances and functional ingredients of apple juice by lactic acid bacteria fermentation

This study aimed to analyze the influence of lactic acid bacteria fermentation on the aroma composition and functional composition of apple juice,selected Lactobacillus reuteri to ferment apple juice,used HS-SPME-GC-MS and HPLC to analyze the changes of volatile aroma composition,organic acids and phenols after fermentation.The results showed the best fermentation time was about 18 h;The type and content of volatile substances(mainly alcohols and esters)in fermented juice changed and affected the overall aroma;The content of organic acids such as succinic acid,tartaric acid,malic acid and pyruvic acid affected the taste and flavor;The content of polyphenols such as gallic acid and protocatechuic acid increased,which enhanced the antioxidant capacity and functionality of fermented juice.This result showed the positive effect of fermentation on juice and provided a reference for the subsequent research on the aroma and functional composition of apple juice.

Research on the Construction and Function of a Chlorophyll Degradation Recombinant Engineering Strain

In order to effectively reduce the chlorophyll content in flue-cured tobacco, improve the overall quality of tobacco leaves, chlorophyllase gene was cloned from Arabidopsis thaliana. After the expression of the expression vector in E. coil, the recombinant engineering strain was obtained. Afterwards, IPTG （isopropy-β-D-thiogalactopyranoside）was used to induce the goal protein, and the chlorophyllase activity of the recombinant engineering strain was measured, so as to investigate its degradation effect on the chlorophyll in the extracts of tobacco leaves. The results were as follows： （1） the amplified chlorophyllase gene At- CLH1 constructed the expression vector pET28a-AtCLH1 successfully, obtaining the recombinant engineering strain; （2） induced under 30 ℃ for 22 h, the strain could well express the recombinant protein AtCLH1 with 0.5 mmol/L IPTG, and the molecular weight was about 35 kDa; （3） the strain showed good chlorophyllase producing capability, and the activity of the produced chlorophyllase could reach up to 24.9 U/mL, which could degrade the chlorophyll in tobacco extract and had a good application prospect in improving the quality of low quality tobacco; （4） based on the results of orthogonal test, the enzyme extract from the strain was added to the tobacco leaf surface, which could make the degradation rate of chlorophyll in the tobacco leaf reach 17.06% under the temperature of 37 ℃ at the humidity of 75% for 48 h; （5） after treated by the enzyme liquid, the test tobacco showed increase in the content of aromatic substances, enhancement of tobacco fragrance quality and amount, significant decrease of offensive odor and irritation, significant improvement of agreeable aftertaste, making the overall sensory quality of the tobacco leaf significantly improved.