Digestive And Glycolytic Properties Of Dietary Fiber-conjugated Phenol, A By-product Of Lychee Juice, And Its Effect On Bread Dough Quality

Lychee(Lychee chinensis Sonn.)is a tropical and subtropical fruit.Because its mature period is in the rainy season,the fruit is easy to spoil after picking.The nuomici lychee pulp juice by-product was used as raw materials in this study,which is common on the market.The effects of heat pump drying and superfine grinding on the composition and content of bound phenols in dietary fiber were investigated.The effects of simulated digestion and colonic fermentation on the release and fermentation of bound phenols in lychee pulp juice by-product were investigated,and the effects of different particle sizes of lychee pulp juice by-product powder on the gas holding capacity of bread dough fermentation were analyzed.(1)The effects of drying methods(heat pump and hot air drying)and grinding methods(Superfine and ordinary grinding)on the physical properties,dietary fiber bound phenol content and composition,morphology and microstructure of lychee pulp juice by-product were analyzed.Scanning electron microscope analysis showed that after hydrolysis,lychee pulp pomace powder became loose and broken.Differential calorimetric scanning analysis showed that the thermal stability of lychee pulp pomace before hydrolysis was much higher than that after hydrolysis.Fourier transform infrared spectroscopy(FTIR)confirmed the structure change of lychee pulp pomace powder after extraction with phenol.In addition,the water holding capacity,water solubility and swelling property of superfine grinding lychee pulp pomace powder were higher than those of ordinary grinding lychee pulp pomace powder,but the oil holding capacity was weaker than that of ordinary grinding lychee pulp pomace powder.The results of bound phenol content determination showed that the content of bound phenol of lychee pulp pomace dried by heat pump with the same grinding method was higher.Eleven kinds of bound phenolic compounds were identified by liquid chromatography.The highest content of bound phenolic compounds was found in lychee pulp pomace dried by heat pump.The results of liquid-mass analysis showed that gallocatechin was produced from lychee pulp pomace by heat pump drying and superfine grinding.In conclusion,after heat pump drying and superfine grinding treatment,the content of bound phenol of lychee pulp pomace increased and its physical properties changed,which provided a theoretical basis for the product development of lychee pulp pomace.(2)Three particle sizes that have significant difference of lychee pulp juice by-product powder were prepared by ordinary grinding and superfine grinding.The release of bound phenols from dietary fiber in lychee pulp pomace powder was investigated by simulated digestion(independent simulated saliva,simulated gastric,simulated intestinal juice and continuous simulated oral gastrointestinal digestion)and colonic fermentation.The results showed that the content of free phenol in simulated gastric and simulated intestinal juice digested samples was significantly higher than that in simulated saliva digested samples and the content of phenolic substance in continuous simulated gastrointestinal digestion sample was significantly higher than that in segmented independent simulated digestion sample.The content of phenolic substance and antioxidant capacity of lychee pulp pomace powder with smaller particle size were higher under the same digestion mode.Colonic fermentation was more conducive to the release of phenolic compounds in lychee pulp pomace powder than simulated digestion,and had stronger antioxidant activity.Fourier transform infrared spectroscopy confirmed that colon fermentation changed the structure of lychee pulp pomace powder and released phenolic compounds that bound to dietary fiber.The results of gas chromatography mass spectrometry(GC-MS)showed that the short chain fatty acids produced by lychee pulp pomace powder with smaller particle size were more than that with larger particle size.In conclusion,the digestion characteristics of lychee pulp pomace powder with smaller particle size were better.(3)The effects of the amount of lychee pulp pomace powder and the amount of water on the gas holding capacity of bread dough fermentation were investigated through “hybrid constraint experimental design”.Fermentation volume of bread dough of which formula were optimized by hybrid constraint experimental design was determined.Minitab software was used to gragh the mixture contour map and mixture surface map of dough fermentation volume to analyze variation trend of the influence of flour ratio on dough fermentation volume was analyzed.The results of SEM showed that the lychee pulp pomace powder with smaller particle size had less influence on the fermentation volume of dough,and the pore of the cross section of dough was larger.The relationship between the content of protein secondary structure in dough and the volume of dough fermentation was investigated by FTIR.It is showed that the by-product powder of lychee juice with small particle size had more α-helix and β-turn and less β-sheet,which is resulted in more stable structure and larger volume of dough.The content analysis of free sulfhydryl group of dough shows that the smaller the particle size of lychee fruit juice by-product powder,the lower the free sulfhydryl group content,the more stable the dough structure and the larger the fermentation volume of the dough.The fluorescence spectrum intensity of dough also confirmed that the small size particle lychee fruit juice by-product powder had lower fluorescence spectral intensity,more stable dough structure and larger fermentation volume.In conclusion,the small particle size by-product powder of lychee juice is more suitable for adding in bread and increasing the content of combined phenol-dietary fiber.