Preparation And Biological Modification Of Dietary Fiber From Lemon Peel Residue

Lemon peel residue is a by-product of lemon processing and utilization,accounting for nearly half of lemon fruit,and is mostly treated as waste.However,it is rich in dietary fiber.If it is not used,it will not only waste a lot of resources,but also cause environmental pollution.As the seventh largest nutrient,dietary fiber has many important physiological effects on human body,such as regulating intestinal function and preventing diseases.It is an indispensable part of people’s daily diet.In this paper,lemon peel residue dietary fiber was prepared with lemon as raw material,and the Soluble dietary fiber（SDF）content in lemon peel residue was improved by microbial fermentation modification,and the effect of microbial modification on lemon peel residue dietary fiber was analyzed.The main research contents and results are as follows:（1）The experimental results of steam and hot air enzyme drying:the lemon peel residue can be dried by steam for 8 minutes;The enzyme was killed by hot air at different temperatures（60℃,70℃,80℃,90℃,100℃and 110℃）for 320min,180min,125min,115min,85min and 75min respectively.The enzyme killing efficiency was not as good as that of steam;The experimental results of drying kinetics of lemon peel residue show that the drying rate of lemon peel residue samples is accelerated with the increase of temperature,which is about 300min or more at 60～70℃,about 200Min or less at higher temperature of 90～110℃,and about 150min at110℃;The energy consumption decreases with the rise of drying temperature.The energy consumption is the highest at 60℃,and the lowest at 110℃,which is about5.78 kw·h;The drying temperature had little effect on the Total dietary fiber（TDF）content of lemon peel residue,but the content of Insoluble dietary fiber（IDF）decreased gradually with the increase of drying temperature,SDF increased gradually with the increase of drying temperature.The SDF of each treatment of steam enzyme inactivation was higher than that of drying enzyme inactivation.At 110℃,the highest SDF content was about 27.0%;The pectin content of lemon peel residue treated with hot air enzymatic treatment increased first and then decreased with the increase of temperature.The pectin content of steam enzymatic treatment increased with the increase of drying temperature.The pectin content of lemon peel residue reached the peak at 110℃,about 18.7%;The pectin content of steam drying at different temperatures was higher than that of hot air drying.After comprehensive consideration,lemon peel residue dietary fiber raw powder was prepared by steam inactivation for10min and drying at 110℃for 135min as the raw material for subsequent experiments.（2）Optimization of biological modification process of lemon peel residue raw powder and comparative analysis of physical and chemical characteristics of modified lemon peel residue dietary fiber experimental results:after the appropriate range of each factor level is obtained through single factor experiment,under the condition that the initial p H of fermentation is natural p H,a three factor and three-level orthogonal optimization experiment is designed,with SDF and IDF as the response values,The optimum fermentation conditions of lemon peel residue dietary fiber by three fungi were determined as follows:（1）Fermentation modification of Mucor（M）:Inoculating7%Mucor and fermenting at 29℃for 84 hours.Under this optimized process condition,the SDF content of lemon peel residue is up to 35.45%.（2）Fermentation modification of Aspergillus oryzae（M‘）:inoculate 8%Aspergillus oryzae and ferment at 31℃for 48hours.Under the optimized process conditions,the highest SDF content of lemon peel residue was 36.96%;（3）Fermentation modification of Aspergillus niger（H）:inoculate7%Aspergillus niger and ferment at 29℃for 72 hours.Under the optimized process conditions,the highest SDF content of lemon peel residue was 37.35%.The lemon peel residue dietary fiber modified by fungi and lactic acid bacteria was obtained by secondary fermentation with Lactobacillus plantarum.Comparing the physical and chemical characteristics of lemon peel residue dietary fiber modified by several different methods,it was found that the basic nutrients such as fat,protein and water in lemon peel residue dietary fiber modified by microbial fermentation decreased;The contents of SDF,total acid,reducing sugar and total flavonoids of lemon peel residue dietary fiber fermented by fungi combined with Lactobacillus plantarum were significantly higher than those of fungal fermentation and Lemon peel powder（CK）alone.The combined fermentation of Aspergillus niger+Lactobacillus plantarum（HR）was better.The contents of SDF,total acid,reducing sugar and total flavonoids were39.26%,23.85%,2.3%and 16.61mg/g respectively;The total antioxidant capacity of modified lemon peel residue dietary fiber was improved.The total antioxidant capacity of modified lemon peel residue dietary fiber by H and HR fermentation was the strongest,which were 55.16±0.23mg/ml and 45.32±0.21mg/ml respectively.The particle size and microscopic observation showed that the microbial fermentation modification could reduce the particle size of lemon peel residue dietary fiber to varying degrees,and the surface of lemon peel residue dietary fiber particles showed honeycomb structure.The fermentation modification of fungi combined with Lactobacillus plantarum was better than that of single fungus.The minimum particle size of lemon peel residue dietary fiber treated with HR was about 47.45μm.The structure is more loose and honeycomb is more obvious.In conclusion,microbial fermentation modification can effectively improve the physical and chemical properties of lemon peel residue dietary fiber.The effect of fungi combined with Lactobacillus plantarum is better,and the combined fermentation of HR is better.（3）Comparative analysis of food chemical characteristics of microbial modified lemon peel residue dietary fiber and its application in biscuits:the analysis of food chemical characteristics shows that the modification improves the hydration properties of lemon peel residue dietary fiber,such as water holding capacity,expansibility and water solubility index;The adsorption capacity of modified lemon peel residue dietary fiber for nitrite ions and cholesterol increased under simulated human gastric juice environment（p H=1.5）and small intestine environment（p H=7.6）.The adsorption of NO₂^-was mainly carried out in acidic environment,and the adsorption capacity of M for NO₂^-was the strongest,about 27.61μg/g,the adsorption capacity of cholesterol in neutral environment is stronger than that in acidic environment,and the adsorption capacity of HR for cholesterol is the highest,about 31.40mg/g.These changes can provide support for the application of modified lemon peel residue dietary fiber in the development of food products and health food.Therefore,the application of modified lemon peel residue dietary fiber in biscuits was studied.The results showed that the addition of lemon peel residue dietary fiber had no effect on the alkalinity of biscuits,and could improve the elasticity and viscosity of dough to varying degrees,with H and HR being the best;The water holding capacity of biscuits prepared by adding fungus combined with Lactobacillus plantarum fermentation modified lemon peel residue dietary fiber is higher than that of single fungus fermentation modified lemon peel residue dietary fiber,which is higher than CK,and the water holding capacity of HR is the highest,about 160.40%.Adding modified dietary fiber can not only improve the texture characteristics of biscuits,increase the hardness of biscuits and reduce the brittleness of biscuits.At the same time,it is also helpful to improve the sensory quality of biscuits.In conclusion,the biological modification of lemon peel residue dietary fiber by fungi combined with Lactobacillus plantarum fermentation is better than that by single fungi,and the fermentation of Aspergillus niger combined with Lactobacillus plantarum is relatively better.