| In this study,hawthorn fruit was selected as raw material to extract hawthorn polysaccharide by hot water extraction method.After extraction,the polysaccharide was purified using an anion-exchange chromatography of DEAE-52.All elution peaks were collected and concentrated,dialyzed and lyophilized.The neutral sugar(WPS)and acidic sugar(SPS-2),which were the most abundant components in the eluted fraction,were measured for monosaccharide composition and antiglycation activities in vitro.Then,the hawthorn pectin with strong antiglycation activity was degraded by enzymatic method and ultrasound-assisted enzymatic method respectively.The degradation products were fractionated into low,medium and high molecular weight pectin oligosaccharides,respectively,and the monosaccharide composition of each pectin oligosaccharide was determined.On this basis,the antiglycation activities of each pectin oligosaccharide was determined,and the components with better antiglycation activities were selected for molecular composition and prebiotic activities in vitro.Finally,hawthorn pectin oligosaccharides with high antiglycation and probiotic activities were added to bovine milk at 1%,3% and 5% respectively to make yoghurt,and the effects of different oligosaccharides on yoghurt were compared,including total AGEs content,viable bacteria number,protein content,reducing sugar content,water holding capacity,sensory and acidity.The results are as follows:1.The results of preparation and composition analysis of hawthorn pectin oligosaccharides showed that: 1)hawthorn polysaccharide was separated and purified by ion exchange column DEAE-52 to obtain four elution components,including neutral sugar WPS and acid sugar SPS-1,SPS-2 and SPS-3.Among them,WPS and SPS-2 had the highest content.The results of monosaccharide composition showed that the total sugar content of the WPS component(96.8%)and SPS-2 component(97.4%)were higher,but the uronic acid content of SPS-2 was much higher than WPS,75.2% and 0.7%,respectively.The main monosaccharides of WPS were galactose(37.1%),glucose(25.8%),arabinose(14.1%)and rhamnose(10.3%).The main monosaccharide of SPS-2 were galacturonic acid(71.9%),arabinose(16.9%),rhamnose(3.4%)and galactose(1.7%).2)In the determination of antiglycation activities in vitro,the antiglycation activity of SPS-2 was significantly higher than that of WPS,so the SPS-2 component was selected for further degradation.3)Whetherit was enzymatic or ultrasound-assisted enzymatic degradation,the largest yield of SPS-2 degradation products was medium molecular weight pectin oligosaccharide(MM-POS),whose main monosaccharide composition was galacturonic acid.However,different degradation methods had great influences on the content of galacturonic acid,and the galacturonic acid content of low molecular weight pectin oligosaccharide(LM-POS)in the products of enzyme degradation was much larger than that of high molecular weight pectin oligosaccharide(HM-POS),the galacturonic acid content of LM-POS and HM-POS in ultrasonic-assisted enzymatic degradation products were very close and accounted for about half of the monosaccharide composition.2.The results of antiglycation and probiotic activities in vitro of hawthorn pectin oligosaccharides showed that: 1)Whether it was enzymatic or ultrasound-assisted enzymatic degradation,the antiglycation activity of MM-POS was higher than that of LM-POS and HM-POS.The antiglycation activity of MM-POS from enzymatic degradation was stronger than that of MM-POS from ultrasound-assisted enzymatic degradation.2)Two MM-POS with better antiglycation activity were selected for molecular composition analysis.The results showsd that the medium molecular weight pectin oligosaccharide samples obtained by enzymatic degradation(E-MM)had the highest content of polygalacturonans,and these polygalacturonans were found both in free and in methylated/acetylated forms,and some were also detected in unsaturated form.In the sample of medium molecular weight pectin oligosaccharide obtained by ultrasonic assisted enzymatic degradation(UE-MM),the content of polygalacturonans was also the highest,but it was lower than that in enzymatic degradation,and the degree of methylation and acetylation was also decreased.In addition,the neutral sugar content(including arabinose and rhamnose)was significantly increased in the MM-POS obtained by ultrasound-assisted enzymatic degradation,compared to that by enzymatic degradation alone.3)At 48 h of fermentation,the levels of total short-chain fatty acids(SCFA),acetic acid and butyric acid of UE-MM were higher than those of E-MM.Therefore,UE-MM had relatively strong in vitro fermentation capacity,and its prebiotic activities in vitro was higher than that of E-MM.Therefore,UE-MM was selected as the pectin oligosaccharide with high antiglycation and probiotic activities in vitro,which was added into milk for fermentation experiment.3.The application results of hawthorn pectin oligosaccharides in yoghurtshowed that different proportions of 1%,3% and 5% hawthorn pectin oligosaccharides were added to milk and fermented to produce yoghurt.The yoghurt curd time,total AGEs content,viable bacterial count,protein content,reducing sugar content,water holding capacity,sensory evaluation and acidity had different effects.In the process of yoghurt fermentation,oligosaccharides played a certain role in promoting the process of yoghurt fermentation.When the addition of oligosaccharide was 3%,yoghurt had the fastest curd speed,the largest number of viable lactic acid bacteria,the highest water holding rate and the best sensory evaluation.when the addition of oligosaccharide gradually increases within the scope of this study,yoghurt had the lower total AGEs content and the higher the reducing sugar content.In summary,hawthorn pectin oligosaccharides could inhibit the generation of AGEs in the fermentation process of yoghurt,and the best yoghurt product was obtained when the amount of oligosaccharides was 3%. |
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