Quality Improving In Cloudy Apple Juice:Innovative Clean Label Concept

The stability of fresh pressed apple juice and the enzymatic Browning led by polyphenol oxidase(PPO)are two important factors limiting the development of not from concentrated(NFC)apple juice industry.Traditional physical and chemical methods are easy to have problems such as poor safety,difficult extraction and serious flavor loss.Therefore,based on the concept of clean label,hawthorn and sea-buckthorn were selected as natural ingredients to be added to apple juice in this paper to explore their potential to replace traditional additives in improving the stability of apple juice and controlling enzymatic Browning.At the same time,based on the improved compound juice products,the effects of two most commonly used thermal sterilization methods in actual processing,pasteurization and ultra-high temperature instantaneous sterilization(UHT),on the quality of compound turbified juice were studied.The main research contents and results are as follows:1.Hawthorn has a high pectin content and viscosity,and has the potential to be used as a natural stabilizer.Therefore,in this study,2%,4% and 6%(W/W)of fresh fruit of Hawthorn were mixed with apple juice to explore the stability improvement effect of hawthorn on apple juice.The results showed that hawthorn could effectively improve the suspension stability of fruit juice and inhibit the stratification of fruit juice.The addition of hawthorn significantly increased the cloud stability,cloud value,accelerated centrifugal stability and surface viscosity of fruit juice samples,and decreased the centrifugal precipitation rate of apple juice samples.The rheological analysis and texture analysis of the samples after gel showed that the rheological properties of the samples were stable,and the gel strength and gel ability basically increased with the increase of the added amount of hawthorn.Therefore,adding 2%-6%hawthorn can effectively improve the stability of apple juice,and when the content is higher than 6%,it has the potential as a new type of jelly product.2.Hippophae buckthorn is rich in antioxidant substances and has the potential to be used as an effective Browning inhibitor.Therefore,in this study,3%,5% and 7%(W/W)sea-buckthorn juice were added to apple juice to explore the anti-browning effect of sea-buckthorn on apple juice.The results showed that sea-buckthorn could effectively control the Browning of fruit juice and inhibit PPO activity of apple juice.The polyphenol oxidase activity and Browning degree of sea-buckthorn and apple juice compound decreased significantly with the increase of sea-buckthorn content.The results showed that the content of ascorbic acid in sea-buckthorn was as high as 480mg/100 g,which was the main factor of inhibiting Browning of apple juice and PPO activity of sea-buckthorn.However,the anti-browning effect of sea-buckthorn was stronger than that of the same amount of exogenic ascorbic acid.Seventeen kinds of phenolic acids and flavonoids were identified by UHPLC-QE-MS.PPO inhibition test showed that coumaric acid,isorhamnetin,myricetin and quercetin were effective PPO inhibitors,among which quercetin showed the strongest inhibitory effect(IC50=10.23?mol/L).It was concluded that the effective inhibition of sea-buckthorn on apple juice was mainly caused by the combined action of phenolic inhibitors such as ascorbic acid and quercetin.Therefore,sea-buckthorn can be used as a natural and effective Browning inhibitor and has a strong application prospect in fruit juice and fruit puree.3.On the basis of the previous two chapters,4%(W/W)of hawthorn and 5%(W/W)of sea-buckthorn were selected and added into apple turbied juice to obtain the compound turbied juice product.The effects of pasteurization(90?/180 s)and UHT(121?/5 s)on the quality of turbified juice were studied.The specific results are as follows: thermal sterilization can completely inactivate PPO,but it will deepen the Browning of tur BID juice and reduce the stability;The effect of thermal sterilization on the physicochemical properties was mainly reflected in the decrease of total phenol and ascorbic acid contents.The efficacy of UHT on the sterilization of juice samples stored at 4? and 25? was much higher than that of pasteurization.The microbial safety of the UHT group could be maintained at 8 weeks(4?)and 21 days(25?),respectively,while the microbial safety of the pasteurization group was damaged at 3-5 weeks(4?)and 10-21 days(25?),respectively.In contrast,UHT can retain the aroma components of apple cloudy juice to a greater extent and meet the cleaning label concept.Therefore,in addition to the cold chain 21-day shelf life of short-term storage products,pasteurization is appropriate,and UHT is safer for other application scenarios.