| Flavonoids and pectin are widely found in citrus plants.Flavonoids are polar molecules and therefore are water soluble.Due to plenty of phenolic hydroxyl groups,flavonoids exhibit weak acidity and it is easy for them to dissolve in alkaline solutions.Therefore,extraction of flavonoids with alkaline solutions is considered as an effective and environmental friendly method since organic solvents are excluded in such extraction.The residuals are then washed with acidic solutions to extract pectin,which would increase the efficient utilization of the raw materials.Successive extractions of flavonoids and pectin through sequential applications of alkaline and acidic solutions significantly reduced the consumption of organic solvents and the effluents can be neutralized to reduce the environmental pollution and risk.As the development of the society and the improvement of living levels,the concepts and ideas of consumption of Chinese people has been modified.As a result,there are increasing demands for new food stuffs with low sugar and low calories nowadays.According to such a tendency,LMP exhibits strong potential in food industry.However,due to the limitations of current production conditions and technology,there is a lack of production of LMP.It is of great urgency and importance to establish a method to convert HMP to LMP effectively and efficiently.Shatian pomelo peels were used as raw materials in this research.According to the properties of flavonoids and pectin,successive extractions with alkaline and acidic aqueous solutions were performed to obtain flavonoids and pectin sequentially.Extraction temperature,time,pH and solid-liquid ratio were selected as single-factor variables,and the technical parameters for extraction process of flavonoids and pectin were studied,respectively.Quadratic polynomial models for predicting the extraction yields of the two products under various conditions were established through response surface method.At the same time,low methoxyl pectin was prepared from the extracts and the quantity of hydrogen peroxide,pH and pectin mass used for the conversion were selected as single factor variables.The results are as follows:(1)According to the extraction yields and the chemical properties of flavonoids and pectin,the sequence that flavonoids were firstly extracted with alkali and then pectin was extracted with acid was confirmed.(2)The extraction time(A),pH(B)and extraction temperature(C)were selected as independent variables,while the extraction yield of flavonoids(Y)was treated as a dependent variable.A quadratic polynomial model was established through response surface: Y = –288.368 + 4.934A+3.824B+1.385C+0.0375 AB +0.1065BC–0.0255A~2–5.735B~2–0.0105C~2.The corresponding optimal extraction conditions were determined as(extraction time)= 129 min,(extraction temperature)= 61.2?,and(extraction pH)= 8.8 with the solid-liquid ratio set as 1:16.The optimal extraction yield of flavonoids was predicted as 0.435%.(3)The extraction time(A),pH(B)and extraction temperature(C)were selected as independent variables,while the extraction yield of pectin(Y)obtained from the residuals after first extraction was treated as a dependent variable.A quadratic polynomial model was established through response surface:Y=–288.368+4.934A+3.824B+1.385C+0.0375AB+0.1065BC–0.0255A~2–5.735B~2–0.0105C~2.The corresponding optimal extraction conditions were determined as(extraction time)= 100 min,(extraction temperature)= 80.1?,and(extraction pH)= 1.4 with the solid-liquid ratio set as 1:30.The optimal extraction yield of pectin was predicted as 16.88%.(4)It was found that the pectin extracted from the above method was highly methoxylized,and therefore it was treated by hydrogen peroxide.The mass of pectin(A),the quantity of hydrogen peroxide(B)and pH(C)involved in the demethoxylization were selected as independent variables,while the degree of pectin methoxylization(Y)was treated as a dependent variable.A quadratic polynomial model was established through response surface: Y=0.56–0.031A–0.16B–0.022C–0.023AB+0.014AC–0.011 BC + 0.022A~2–0.096B~2.(5)According to the determination by HPLC,the major component of the flavonoids extracted from the Shatian pomelo peels was Naringin and Neohesperidin. |
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