Enzymatic Modification Of Chia Seed (Salvia Hispanica L.) Dietary Fiber And In Vitro Digestion

In recent years,chia seed has attracted more and more attention due to its polyunsaturated fatty acids,dietary fiber,high-quality protein,and polyphenols.The culinary uses of chia seeds were equally diverse,including whole seeds,seed oil,seed mucilage and seed flour.It is well known that the nutritional value of food not only depends on its composition but also its bioavailability.While seed flour could improve bioavailability,it also leads to a loss of nutrients,especially polyunsaturated fatty acids.Hence,the whole chia seed is a common way to consume,which can be added directly to milk,juice and other drinks.However,chia seeds are so small that can be swallowed when added to drinks.And the structural integrity of seeds could not be destroyed during oral digestion.Therefore,it is of great significance to explore the changes of whole chia seeds during gastrointestinal digestion for consumption and processing.In this study,the changes of structure,physicochemical properties and functional properties of whole chia seeds during digestion were investigated by static in vitro digestion method.Then,the dietary fiber of seed coat was modified by different enzymatic methods,and the modification conditions were optimized by single factor experiment and response surface experiment.The effects of different enzymes on the physicochemical,functional and digestive properties of whole chia seeds were further studied.The main studies and results are as follows:(1)The nutrients degradation,structural and functional characteristics of whole chia seeds during simulated in vitro digestion were investigated.After gastrointestinal digestion,the digestibility of lipid and protein was 0.46% and 11.38%,respectively.The microscopic results(optical microscopy,laser scanning confocal microscopy and scanning electron microscopy)demonstrated that the seeds remained intact after digestion,and the mucilage adhered tightly to the seed coat during digestion.The reason affecting the nutrients release was the existence of sclereid layer.The water holding capacity and oil holding capacity of seeds accounted for 6.37g/g and 3.28 g/g after intestinal digestion.Fourier transform infrared spectroscopy indicated that chia seed mucilage still had polysaccharide properties after gastrointestinal digestion.In order to improve bioavailability of chia seeds,pretreatment is important.(2)In order to reduce the content of insoluble dietary fiber in chia seed coat and make the whole chia seed easier to be absorbed and utilized by human body,the dietary fiber of whole chia seed was modified by cellulase,xylanase and amylase,respectively.Taking the soluble dietary fiber yield and chia seeds content as index,the experimental conditions were optimized by single factor experiment.The optimal conditions of cellulase were as follows: cellulase enzyme addition 900 U/g,solid-liquid ratio 1:20,p H 5.0,50℃,6 h.The optimal conditions of xylanase were as follows: xylanase enzyme addition 900 U/g,solid-liquid ratio 1:25,p H 5.0,50℃,10 h.The optimal conditions of amylase were as follows: amylase enzyme addition 60U/g,solid-liquid ratio 1:25,p H 6.0,50℃,9 h.Based on best modification conditions of three single factor experiments,cellulase was chosen to combine with xylanase and amylase,respectively,and further optimized by response surface methodology.Firstly,compound cellulase and xylanase.The optimal conditions were as follows: the ratio of cellulase to xylanase was 2.22:1,the reaction time was 8.44 h,and the reaction temperature was 48.7℃.Secondly,compound cellulase and amylase.The optimal conditions were as follows: cellulase addition was 621 U/g,amylase addition was 55 U/g,and reaction time was 5.74 h.The results showed that enzymatic modification of chia seed insoluble dietary fiber was effective,and the complex enzyme of cellulase and amylase was the best.(3)The physicochemical properties,functional properties and digestive properties of chia seeds modified by enzymes were compared and analyzed.The results showed that the contents of fat and lignin were significantly increased(P<0.05).And there were no significant differences(P>0.05)in protein contents.At the same time,the contents of cellulose and hemicellulose were significantly decreased(P<0.05).The mucilage of chia seeds modified by cellulase and amylase decreased significantly by scanning electron microscope.And the Fourier transform infrared spectroscopy showed that the mucilage still had the polysaccharides properties.The water holding capacity and oil holding capacity modified by cellulase were relatively higher,which was 2.91 g/g and 1.57 g/g,respectively.After simulated in vitro digestion,the structure of chia seeds modified by cellulase was the most damaged,and the release rate of fatty acids was 2.30% and that of amino acids was only 0.18%.The results showed that cellulase could degrade more insoluble dietary fiber,and exhibited good functional and digestive properties.In conclusion,we found that the consumption of whole chia seeds would reduce their overall bioavailability by simulated in vitro digestion.The dietary fiber of seed coat was further modified by different enzymatic methods.The chia seeds modified by cellulase had excellent physicochemical,functional and digestive properties,which was beneficial to its further development and application in the field of food processing.