Study On Fatty Acid Composition And Phenolics In Raspberry Seeds

Raspberry(Rubus idaeus L.)has a unique flavor and rich nutrition,and is deeply loved by western consumers.However,the fresh fruits of raspberry have high water content and thin cell walls,which are not easy to transport and preserve.Raspberry is often processed into juice,wine or other products.The raspberry pomace produced in food processing and production was discarded as waste,and led to a waste of raspberry pomace.Raspberry seeds account for ~60% of the pomace,not only rich in unsaturated fatty acids,but also contain many different forms of phenolics.Therefore,this paper uses raspberry seeds as materials.Firstly,the extraction rate and fatty acid composition of RSO with three common extraction methods were compared.Secondly,considering sea buckthorn seed oil(SSO)is included in the list of medicine and food homologous items with raspberry and has been used for industrial production,SSO was used to compare the differences of physical and chemical properties and the stability with raspberry seed oil(RSO)with three common extraction methods.Thirdly,one extraction method was selected to optimize the extraction process by Response surface to improve oil yield.Finally,Raspberry Pomace without seed(RP)was compared with Raspberry Seed(RS)to extract free,soluble-bound and insoluble-bound phenolics,and the antioxidant activity and enzyme inhibitory activity of different phenolic fractions were measured.With a view to comprehensively develop and utilize the fatty acids and phenolics in raspberry seeds.The main contents were as follows:(1)The RSO was extracted by three methods: Ultrasonic-Assisted Extraction with Ethanol(UAE-E),Ultrasonic-Assisted Extraction with hexane(UAE-H)and Soxhlet Extraction with hexane(SE-H);and the extraction rate,fatty acid composition,antioxidant activity and total saponin contents were measured.The results were showed that the UAE-E method has the highest RSO extraction rate of 18.55%,and the extraction rates of UAE-H andSE-H were 10.18% and 13.58%.However,the RSO of UAE-E method has many impurities and poor transparency.According to the results of Gas Chromatography-Mass Spectrometry(GC-MS),a total of 32 compounds were identified in these RSO.The contents of unsaturated fatty acids(linoleic acid and linolenic acid,etc.)in RSO with UAE-E,UAE-H and SE-H were82.71%,85.76% and 88.83%,respectively,all > 80%;the ratio of ?-6/?-3 fatty acids was2.32:1,2.27:1 and 2.22:1,respectively.Study on DPPH· scavenging activity has shown that the RSO with UAE-E has the strongest scavenging ability.Therefore,UAE-E method has the highest RSO extraction rate and antioxidant activity,but there was many impurities.The RSO with SE-H method has a high content of unsaturated fatty acids and the lowest ratio of?-6/?-3 fatty acids.The RSO with different extraction methods has different characteristics and can be extracted according to different uses.(2)UAE-E,UAE-H and SE-H were used to extract RSO and SSO,and the 10 physical and chemical properties were determined.Through time gradient experiment,the changes of physical and chemical properties of RSO and SSO with UAE-H method were compared to determine their stability.The results were showed that the RSO with UAE-E has poor transparency and some sediments,and that with UAE-H method was more clear.For RSO,the acid value,iodine value,saponification value and peroxide value of UAE-H method were0.88,1.13,1.01 and 0.25 times of SE-H method,respectively;for SSO,UAE-H method were1.03,1.14,1.31 and 1 times of SE-H method.It was indicated that the oil with ultrasonic extraction has better physical and chemical properties than that with soxhlet extraction.Time gradient experiments showed that the acid value,iodine value,saponification value and peroxide value of RSO were changed by 1.10,1.26,1.26,and 11.1 times in 0 ~ 8 months;SSO were changed by 1.02,1.35,1.15 6.19 times.The acid value and peroxide value of RSO and SSO continue to increase,while the iodine value and saponification value decrease.Therefore,hexane is more suitable as a solvent for extracting RSO and SSO.The oil with ultrasonic extraction has better physical and chemical properties than soxhlet extraction.RSO has the potential for development and production and wide application prospects as SSO.(3)Based on the results of physical and chemical properties,UAE-H was selected tooptimize the extraction of RSO,and the extraction process was optimized by response surface in order to extract RSO efficiently.The material-liquid ratio and the time,temperature and power of the ultrasonic extraction were selected as independent variables.The extraction rate of RSO was the response value.A four-factor three-level response surface design was carried out and the best extraction process was: material-liquid ratio 1:35 g/mL,ultrasonic time 32 min,ultrasonic temperature 45?,ultrasonic power 175 W.At this extraction process,the extraction rate of RSO is 11.1%.(4)In order to further utilize the RS after oil extraction,RP was used as a comparison.Free,soluble-bound(esterified and glycosylated)and insoluble-bound phenolics were extracted from RP and RS through acid and alkali treatment.The total phenolic content and DPPH radical scavenging activity of different phenolic fractions in RP and RS were followed:free > esterified ? insoluble-bound > glycosylated.The sum total phenolic contents of four fractions were 24.14 and 25.40 mg GAE/g dry weight in RP and RS,respectively,which was higher than the sum total phenolic content of common solvent extraction.RS esterified phenolics has the strongest tyrosinase inhibitory activity(TIA)equivalent to the TIA of 1.57 mM ascorbic acid.Moreover,18 phenolics from RP and RS were quantified by high performance liquid chromatography-mass spectrometry(HPLC-MS).Only RS esterified phenolics contained p-hydroxybenzoic acid.Among 15 phenolics,quercetin,chlorogenic acid,and p-hydroxybenzoic acid had obvious promoting effects,while catechin,epicatechin,and caffeic acid exhibited a significant background effect in tyrosinase inhibition activities.The high tyrosinase inhibitory activity of RS esterified phenolics may be related to p-hydroxybenzoic acid.Therefore,the separation of different phenolic fractions of RP and RS increases the total phenolic content,and RS esterified phenolics has a higher TIA,which is significantly higher than other phenolic fractions.The development and application of phenolics in defatted raspberry seed have a guiding role.