| Mulberry is a fast-growing perennial deciduous woody economic plant in the genus Moraceae.The leaves and fruits of mulberry are rich in a variety of natural active ingredients with outstanding nutritional value and functional effects,which are widely used in food,feeds,health products,medicines and other fields.Mulberry trees are planted in a large area in our country,and the output of mulberry leaves and mulberry fruits is huge.At present,mulberry leaves are mainly used for feeding silkworms and feed processing,and most of mulberry leaves have not been fully utilized.The thin skin,juicy,fragile of mulberry fruits make it difficult to be stored for a long time,and they are mostly processed into low value-added products such as beverages and jams.In this thesis,the leaves and fruits of mulberry were used as raw materials,and the key technologies of new green solvents for efficient extraction of active components and microorganism fermentation of mulberry leaves and fruits have been systematically studied.It provides an important research basis and technical support for the high value-added processing and utilization of mulberry resources in our country,and has a wide range of application development value and potential.The main research contents are summarized as follows:(1)The green extraction technology of ultrasonic-assisted surfactant aqueous solution extraction of active components from mulberry leaves was established,and the extraction mechanism was discussed.The extraction process was optimized by solvent screening,single factor experiments and Box-Behnken combined response surface design using surfactant aqueous solution as the extraction solvent and the extraction yields of mulberry leaves total phenols and total alkalids as the indicators.Under the optimal condition,the extraction yields of mulberry leaves total phenols and total alkalids were 24.39 mg/g and 2.97 mg/g,respectively.The six common compounds of phenols and alkaloids in mulberry leaves were quantitatively analyzed.Compared with the traditional organic solvent extraction method and water extraction method,the extraction yields of this method was higher,which was 1.08-2.07 times of ethanol extraction method and 1.17-1.54 times of water extraction method,respectively.By fitting the kinetic model of the extraction process,it was indicated that the extraction method conformed to the second-level kinetic model,and the model parameters were also better than the traditional two methods.The molecular docking results showed that the Triton-114 was interlinked with the target compounds through hydrogen bonding to extract the target compounds from plants.According to the phenomenon of cloud point separation,after heating at 65? for 20 min,the active components in the surfactant extract solutions were preliminarily separated and enriched.(2)The biotransformation rules of active components in mulberry leaves were analyzed through microorganism fermentation,the technical parameters of mulberry leaves fermentation by Monascus and yeast were established,and the activity of fermented mulberry leaves was evaluated.The fermentation conditions of mulberry leaves by complex microorganisms were optimized.The total phenol content of mulberry leaves reached 34.62 mg/g on the 5th day,and the contents of quercetin and kaempferol reached 3.11 mg/g and 1.10 mg/g on the 7th day.The activities of four hydrolytic enzymes that affected the release and transformation of phenolic compounds during the fermentation process were determined.The results indicated that the enzyme activity was related to the composition.Morphological observation showed that the structure of mulberry leaves was seriously damaged after microbial fermentation,and fermentation promoted the release and transformation of active components.The scavenging rate of DPPH and ABTS free radicals and ?-glycosidase inhibitory activity were positively correlated with the contents of total phenols,quercetin and kaempferol in mulberry leaves fermentation.Total phenols contents were closely related to DPPH and ABTS free radical scavenging rate,and quercetin and kaempferol contents were closely related to ?-glycosidase inhibitory activity.(3)The green extraction technology of high-speed homogenization combined with negative pressure cavitation-assisted deep eutectic solvent extraction of mulberry fruits anthocyanins was established.and the stability of anthocyanins in solvents was studied.The natural deep eutectic solvent composed of choline chloride-citric acid-glucose with molar ratio of 1:1:1 and water content of 30%(v/v)was used as the extraction solvent.The parameters were screened and optimized by Plackett-Burman design and Box-Behnken design.Under the optimal condition,the extraction yield of anthocyanins from mulberry could reach 6.05 mg/g.By comparison,the anthocyanins extraction yield from mulberry fruits of this method was better than that of the negative pressure cavitation-assisted deep eutectic solvent extraction and the high-speed homogenization combined with negative pressure cavitation-assisted organic solvent extraction,which was 1.08 times and 1.30 times of the other two methods respectively.By fitting the kinetic model of the extraction process,it was indicated that the extraction method conformed to the first-order kinetic model,and the model parameters were also better than those of the other two methods.Compared with the anthocyanins extracted by traditional organic solvent method,the degradation rate of anthocyanins in deep eutectic solvents was lower and the stability was higher.The deep eutectic solvents were beneficial to the stable extraction and preservation of anthocyanins.Macroporous resin AB-8 was used to enrich the anthocyanins of mulberry fruits extracted by deep eutectic solvent.After resin enrichment,the recovery rate of anthocyanins was 83.57%,the content of anthocyanins in the enrichment of mulberry fruit was 21.64%,and a high purity mulberry fruits anthocyanin enriched product was obtained.(4)The influence factors of immobilized microorganism fermentation of mulberry fruits were investigated.The process of immobilized lactic acid bacteria fermentation of mulberry fruits was established,and the quality of fermented mulberry fruits was evaluated.Firstly,the preparation conditions of immobilized lactic acid bacteria were optimized.After optimization,the microbial embedding rate was 86.73%.Using total phenols and total anthocyanins as indicators,the process of mulberry fermentation by immobilized lactic acid bacteria was optimized.After optimization,the contents of total phenols and total anthocyanins in mulberry fruits fermented by immobilized lactic acid bacteria were 2.93 mg/mL and 2.18 mg/mL,respectively.Compared with unfermented mulberry fruits,the total phenols were slightly increased by 2.81%,and the anthocyanin retention rate was 91.98%which was higher than that of the free lactic acid bacteria fermentation with 71.35%.The antioxidant activity of fruits was evaluated,and the results showed that the antioxidant activity of mulberry fruits fermented by immobilized lactic acid bacteria was higher than that of unfermented mulberry fruits.During low-temperature storage,the total phenols of unfermented fruits and mulberry fruits fermented by immobilized lactic acid bacteria did not change significantly,while the anthocyanins of unfermented mulberry fruits was significantly reduced.The anthocyanin retention rate was 74.57%when stored for 30 days,and the anthocyanin retention rate of the fruits fermented by immobilized lactic acid bacteria could reach 87.79%under the same conditions,and the retention rate increased by 15.22%.The repeated fermentation of mulberry fruits by immobilized lactic acid bacteria was studied.The results showed that the colony number of the immobilized lactic acid bacteria in the pellet was 83.32%after 5 times of use,and the immobilized lactic acid bacteria had good stability and repeatability. |
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