The Change of Total Anthocyanins in Blueberries and Their Antioxidant Effect After Drying and Freezing

This study examined the effects of freezing, storage, and cabinet drying on the anthocyanin content and antioxidant activity of blueberries (Vaccinium corymbosum L). Fresh samples were stored for two weeks at 5(°)C while frozen samples were kept for up to three months at −20(°)C. There were two drying treatments, one including osmotic pretreatment followed by cabinet drying and the other involving only cabinet drying. Total anthocyanins found in fresh blueberries were 7.2 ± 0.5 mg/g dry matter, expressed as cyanidin 3-rutinoside equivalents. In comparison with fresh samples, total anthocyanins in untreated and pretreated dried blueberries were significantly reduced to 4.3 ± 0.1 mg/g solid content, 41% loss, and 3.7 ± 0.2 mg/g solid content, 49% loss, respectively. Osmotic treatment followed by a thermal treatment had a greater effect on anthocyanin loss than the thermal treatment alone. In contrast, the frozen samples did not show any significant decrease in anthocyanin level during three months of storage. Measurement of the antioxidant activity of anthocyanin extracts from blueberries showed there was no significant difference between fresh, dried, and frozen blueberries

Effects of preconditioning on quality of dried blueberries

Blueberries are a rich source of phenolic compounds, especially anthocyanins, which contributes to their high level of antioxidant activity. However, these compounds of significant health benefit will be degraded after the blueberries undergo various air drying processes. Drying of blueberries can be difficult due to the wax layer surrounding the fruit. The health properties may be reduced to a large extent due to long exposure to high temperature. In this study, a mechanical wax abrasive pretreatment is used to carefully remove the wax layer and reduce drying time. The abrasive drum was lined with medium grain sand paper and attached to a constant speed rotator. The amount of blueberries and the rotating time were optimized to reduce the damage to the blueberries. Rabbiteye blueberries cv. Climax were used as the test fruit. A laboratory scale cabinet dryer was operated at temperatures between 50 and 90ºC with single stage and multistage drying strategies. The drying rates, colour and level of phenolic compounds and antioxidant activity were evaluated.Keywords: Blueberries, Air drying, Wax abrasive pretreatmen

2006. The change of total anthocyanins in blueberries and their antioxidant effect after drying and freezing

This study examined the effects of freezing, storage, and cabinet drying on the anthocyanin content and antioxidant activity of blueberries (Vaccinium corymbosum L). Fresh samples were stored for two weeks at 5 • C while frozen samples were kept for up to three months at −20 • C. There were two drying treatments, one including osmotic pretreatment followed by cabinet drying and the other involving only cabinet drying. Total anthocyanins found in fresh blueberries were 7.2 ± 0.5 mg/g dry matter, expressed as cyanidin 3-rutinoside equivalents. In comparison with fresh samples, total anthocyanins in untreated and pretreated dried blueberries were significantly reduced to 4.3 ± 0.1 mg/g solid content, 41% loss, and 3.7 ± 0.2 mg/g solid content, 49% loss, respectively. Osmotic treatment followed by a thermal treatment had a greater effect on anthocyanin loss than the thermal treatment alone. In contrast, the frozen samples did not show any significant decrease in anthocyanin level during three months of storage. Measurement of the antioxidant activity of anthocyanin extracts from blueberries showed there was no significant difference between fresh, dried, and frozen blueberries

Effects of preconditioning on quality of dried blueberries

Abstract Blueberries are a rich source of phenolic compounds, especially anthocyanins, which contributes to their high level of antioxidant activity. However, these compounds of significant health benefit will be degraded after the blueberries undergo various air drying processes. Drying of blueberries can be difficult due to the wax layer surrounding the fruit. The health properties may be reduced to a large extent due to long exposure to high temperature. In this study, a mechanical wax abrasive pretreatment is used to carefully remove the wax layer and reduce drying time. The abrasive drum was lined with medium grain sand paper and attached to a constant speed rotator. The amount of blueberries and the rotating time were optimized to reduce the damage to the blueberries. Rabbiteye blueberries cv. Climax were used as the test fruit. A laboratory scale cabinet dryer was operated at temperatures between 50 and 90ºC with single stage and multistage drying strategies. The drying rates, colour and level of phenolic compounds and antioxidant activity were evaluated

Effects of drying on anthocyanins in blueberries

Blueberries are well known for their high anthocyanin content and the health benefits. Fresh blueberries have limited shelf life and thus are kept frozen or processed. Since freezing is expensive, low cost processing methods, particularly drying are being devised. Various drying treatments were compared with regard to drying time and quality of the dried product in terms of anthocyanin and polyphenolic contents as well as antioxidant activity. The drying treatments involved high temperature in a cabinet dryer and low temperature in a heat pump dryer. Freeze drying was used as a reference treatment. Highbush (Vaccinium corymbosum L., cultivars Crunchie, Star, and Sharpe) and rabbiteye (Vaccinium ashei, cultivars Climax, Powderblue, and Brightwell) blueberries were used in this study. Pre-treatments included osmotic dehydration or skin abrasion. The temperature and concentration of the osmotic solution were the mainparameters contributing to the reduction of drying time. Mechanical skin abrasion was more effective than osmotic dehydration in reducing drying time and minimising the loss of anthocyanin and phenolic contents of the blueberries in air drying treatments. The thickness of cuticle and the structure of epicuticular waxes affected the drying rate of different cultivars of blueberries. Liquid chromatography and mass spectrometry (LC/MS) was used to identify different anthocyanins in the blueberry samples. Delphinidin, petunidin, and malvidin were the main contributors to the total anthocyanin content of the fresh and dried samples. Degradation products of anthocyanins were observed in samples where the anthocyanin contents declined as a result of drying treatments. The anthocyanin content and profile, phenolic content, and antioxidant activity of mulberries (Morus nigra), and Makiang (Cleistocalyx nervosum), a Thai native fruit, were also analysed. There was no significant difference between total anthocyanin content of blueberries and mulberries. In contrast, the total phenolic content and antioxidant effect of mulberry were significantly higher than those of blueberries and Makiang. Skin abrasion and high temperature drying resulted in the fastest drying rate and highest anthocyanin retention. Anthocyanin profiles differed in various cultivars of blueberries. Within the same cultivar, amounts of each anthocyanin varied with pre-treatments and drying methods but the distribution of monomeric anthocyanins was similar