Stability of phenolic compounds and drying characteristics of apple peel as affected by three drying treatments

To realize high-value utilization of discarded apple peel,this study investigated the effects of three selected commercial drying methods on drying kinetics,microstructure,color,phenolic stability and antioxidant capacity of apple peel.Apple peel was dehydrated by hot air drying(AD)at 75,65 and 55℃,heat pump drying(HP)at 65,55 and 45℃,and vacuum freeze-drying(FD),respectively.The results showed that HP was superior to AD and FD in terms of drying rate.In addition,HP at 65℃provided high-quality dried apple peel due to less browning and brighter appearance,the highest retention of total phenolics(29.35 mg/g)and the strongest antioxidant activities,with the highest ABTS and FRAP value of 127.15 and 219.57μmol TE/g,respectively.The content of the six major individual phenolics,i.e.caffeic acid,(-)-epicatechin,hyperoside,rutin,phlorizin and quercitrin,were found to be the highest in HP dried samples.Interestingly,the content of rutin was even increased after HP compared to the fresh sample.Considering drying efficiency,organoleptic quality and phenolic stability of the products,HP at 65°C is suggested for drying of apple peel.

Impacts of different drying strategies on drying characteristics,the retention of bio-active ingredient and colour changes of dried Roselle

The drying kinetics of Roselle （Hibiscus sabdariffa L） of variety Terengganu （UMKL-1） and the quality attribution of Roselle were studied. The experiments were conducted using four different drying methods, including solar greenhouse drying （SD）, solar greenhouse with intermittent heat pump drying （SIHP）, hot air drying （HA） and heat pump drying （HP）. Among the four drying methods, HP achieved the highest drying rate at a range from 0.054 g H20-（g DM）-1. rain-1 to 0.212 g H20-（g DM）-1. rain 1 while SD had the lowest drying rate, measured at 0.042 g H2O. （g DM） 1.min- 1. The analysis on colour kinetics revealed that there is no significant colour loss （p 〉 0.05） observed from HP＇s dried Roselle. Greater amount of flavonoid compounds i.e. protocatechuic acid was found in SD and SIHP dried finished product whereas HP＇s dried Roselle contains higher percentage of catechin as compared to other drying methods.

Dehydration property of Shrimp(Pandalus borealis)undergoing heat-pump drying process

Peeled,headed or whole shrimp(Pandalus borealis)was dried in a heat-pump dryer at-2-0℃and 20℃,respectively,and desorption isotherms characterizing the dehydration property of each shrimp sample group were determined.Desorption isotherms of shrimp handled differently and dried at different temperatures(-2-0℃or 20℃)could be well described by Oswin’s model(X=a(1-a_(w)/a_(w))).The regression model of peeled,headed or whole shrimp was established,which is reliable for predicting the desorption isotherms of shrimp undergoing heat-pump drying.The handling methods of shrimp exhibit measurable influence on desorption isotherms of shrimp,whereas drying temperature(-2-0℃or 20℃)has little influence on the constants of a and n in Oswin’s model,of whole shrimp,even though it has certain influence on these constants of peeled and headed shrimp.For heat-pump drying,headed shrimp may have a better stability than peeled or whole shrimp due to the best stability.

Degradation kinetics of functional components of honeysuckle flowers during controlled-atmosphere heat pump drying

To investigate the change law of functional components and exterior color of honeysuckle flowers(HF)during controlled-atmosphere heat pump drying,nitrogen was used as drying medium in this study to reduce the oxygen concentration.The influences of drying temperature,HF’s loading amount and oxygen concentration on chlorogenic acid content,cynaroside content and L value(on behalf of browning degree)were explored,and the degradation kinetics models of chlorogenic acid and cynaroside were constructed.The results showed that chlorogenic acid content,cynaroside content and L value decreased with the rise of temperature,HF’s loading amount and oxygen concentration.The degradation kinetics models of chlorogenic acid and cynaroside during the drying process were established through introducing an exponent r related to time t in the first order reaction kinetics equation.The models had good fitting precision and can be used to predict the degradation law of chlorogenic acid and cynaroside.

Effects of heat pump drying temperature and dietary fat on carrot β-carotene bioaccessibility

Dehydration can significantly extend the shelf life of dried carrots and still retain nutrition of provitamin A carotenoids.In vitro digestion model was used in this study to assess the effect of drying temperatures of heat pump and dietary fat on the bioaccessibility ofβ-carotene in carrots.Also,low-speed centrifugation was employed to obtainβ-carotene release rate in supernatant.Microfiltration was applied to obtainβ-carotene micellar rate in micelle phase.These assays were used as indicators to assess the bioaccessibility of theβ-carotene.Despite higher drying temperatures had a negative effect on the retention rate ofβ-carotene in carrots,it showed a positive impact on the micellar rate.In addition,dietary fat significantly increased the release rate and micellar rate ofβ-carotene for both fresh carrots and dried carrot products,with the highest release rate and micellar rate obtained when 10%dietary fat was added.Therefore,the heat pump drying process and dietary fat can significantly improve the bioaccessibility ofβ-carotene in carrots,which may increase theβ-carotene bioavailability to human.