| Black garlic is a kind of deep processed product which is made of fresh garlic under controlled high temperatures and humidity with a few days.The garlic turned from white to dark brown with a soft and elastic taste;meanwhile,it eliminated the strong odor and enhanced the physiological activity.Black garlic originates in Japan,and so does its processing technology,which is needed to ferment about 60-90 days and has a long process time with high energy consumption.At present,the black garlic is often processed under variable temperatures.It can shorten the processing time,improve the quality of black garlic and conserve the energy.However,the content of water,reducing sugar and other compositions in black garlic varies significantly due to the different processes.The main functional components in garlic are sulfur compounds and polysaccharides.The polysaccharides accounts for about 75% of the garlic in dry matter.Nowadays,more attention is focused on the allicin and garlic oil,but the study on garlic polysaccharides is relatively rare.Saccharides in fresh garlic is mainly polysaccharides,which is no sweetness to eat.After being processed to black garlic,oligosaccharides and monosaccharides content increased significantly which contributed to a sweet taste.The pathway of these saccharides is still unclear and the effects of black garlic on the constipation mice and intestinal flora are also unknown.In this study,we compared the composition of garlic and black garlic.The neutral polysaccharides were extracted from garlic,and then analyzed characteristics of acid hydrolysis and the probiotic activity.The pathway of saccharides degradation in black garlic was explored.We also used animal experiments to study the effects of black garlic on mice laxative function and the influences on intestinal flora,which not only improve the quality of black garlic but also find new function of black garlic.The main results are as follows:1.The nutrient compositions changed significantly when the garlic was processed into the black garlic.The water and fat content in black garlic decreased with the organic acids,total phenolics and 5-HMF content increased,especially the content of reducing sugar increased from 0.46 g/100 g to 39.49 g/100 g,which improved about a hundred times.The results of eighteen free amino acids were shown that some free amino acid content decreased,resulting in decreasing of the total amino acids contents.2.Garlic crude polysaccharides were purified by DEAE-52 cellulose column and determined by Fourier Transform Infrared Spectroscopy?FITR?,Gel Permeation Chromatographic analysis?GPC?and High Performance Liquid Chromatography?HPLC?.The results showed that the garlic neutral polysaccharide was a polydisperse mixture of oligomers with varying polymerization degree?DP?.Its average molecular weight was 6569 Da with a composition of fructose : glucose = 4:1.Acid hydrolysis experiments of the garlic neutral polysaccharide showed that the lower concentration,the higher temperature and lower pH was attributed to the faster of hydrolysis rate.The hydrolysis kinetics results showed that at the whole stage of nearly neutral pH and initial stage of pH =3,it obeyed first order reaction.3.The oligosaccharides obtained through the hydrolysis and ultrafiltration of garlic neutral polysaccharides.The molecular weight decreased significantly and the oligosaccharides increased during the hydrolysis.The content of saccharides with DP<10 increased from below 15% to above 75%,meanwhile,the monosaccharide content reduced to less than 0.5%,and the average molecular weight of the oligosaccharide was 1444 Da which the average DP was about 8.Compared with garlic neutral polysaccharide,the garlic oligosaccharide obtained had slightly lower ablity to resist the hydrolysis of artificial gastric juice;however,it can significantly promote the proliferation of Lactobacillus,and reduce the pH of the fermentation broth.Therefore,the oligosaccharides obtained from hydrolysis of garlic netural polysaccharides had a stronger probiotic activity.4.The optimal extraction process was drawn through single factor assay and orthogonal test.It was as follows: The material water ratio was 1:12;the extraction temperature was 70 °C and the extraction time was 60 min.The molecular weight distribution of saccharides in garlic and black garlic showed that it mainly ranged 1-15 kDa,among which the ratio of average molecular weight above 4 kDa accounted for more than 80% in fresh garlic.After heated process,it was less than 2 kDa,among which the ratio of average molecular weight less than 1 kDa accounted for about 90% in black garlic.5.The saccharides degradation in black garlic was studied.It was found that saccharides was degradated mainly by high temperatures,and fructan exohydrolase was hardly participated in.The molecular weight of polysaccharides is getting smaller during the heating,and the higher the temperature,the more severely the degradation of polysaccharide.The kinetic analysis showed that it obeyed linear degradation at 70-80 °C and when under 85-90 °C,it deviated linearity.The activation energy was calculated to be 110.56 kJ·mol-1 and the Arrhenius constant was 3.12×1012 h-1.6.Animal experiments on mice showed that black garlic did not cause adverse effects on blood parameters.The black garlic had the laxative effect in constipation mice.It could apparently improve the percentage of propellant in intestinal peristalsis,shorten the time of the first black dejection,increase feces amount and weights in 6 h and improve the water content of mice feces.Black garlic can change the intestinal flora structures and increase the abundance of intestinal flora.At the level of the phylum,it increased the ratio of Bacteroidetes and Proteobacteria,but reduced the ratio of Firmicutes,showing a dominant position tend to Bacteroidetes.In the level of genus,the ratio of Bacteroides,Prevotella and Akkermansia increased,however,the ratio of Lactobacillus and Clostridium decreased.Black garlic can significantly increase the content of butyrate,but do not cause total short-chain fatty acid content increased. |
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