Phytochemical Content and Antioxidant Activity of Malus domestica Borkh Peel Extracts

Apple is an important dietary source of carotenoids and phenolic compounds, and its regular consumption is associated with several health benefits. The aim of this study was to evaluate the phytochemical composition of fresh peels of four red-skinned (“Champion”, “Generos”, “Idared”, “Florina”) and two yellow-skinned (“Golden Delicious”, “Reinette Simirenko”) apple varieties. Antioxidant activity of apple peel extracts was determined by ferric reducing antioxidant power (FRAP) and ABTS radical scavenging capacity assays. Total carotenoid and polyphenolic contents were determined spectrophotometrically, while the profile of individual carotenoids and anthocyanins (in red-skinned varieties) was analyzed using high-performance liquid chromatography coupled to a photodiode array detector (HPLC-PDA). Carotenoid composition was specific for each variety, and total carotenoid content was slightly higher in yellow-skinned apple peels compared to red-skinned varieties. In contrast, total phenolic content was higher in the peels of red-skinned cultivars. Anthocyanin profile was predominated by cyanidin-3-O-galactoside. Antioxidant potential followed the trend of the total polyphenolic content, being highest in “Florina”, as measured by both FRAP and ABTS assays. Our results demonstrated apple peels have high phytochemical content with diverse compositions, and their regular consumption can be an excellent source of antioxidants.

Metabolomic and Transcriptomic Analysis of the Anthocyanin Regulatory Networks in Malus Domestica Borkh. Peel with Different Color Patterns

Background:Coloring is an important external quality of ‘Fuji’ apple (Malus domestica Borkh.) and there are two color patterns of apple peels, i.e., stripe and blush. The objectives of this study were to reveal the anthocyanin biosynthesis metabolic pathway in striped and blushed peels of Malus domestica using metabolomics and transcriptomics, to identify different anthocyanin metabolites, and to analyze the differentially expressed genes involved in anthocyanin biosynthesis.Result:The metabolite concentration and gene expression were profiled in the striped and blushed fruit peels of apple harvested at three ripening periods to elucidate the color formation mechanism. At the green fruit period, there were 83 DAMs,including 30 flavonoids, 674 DEGs (521 up-regulated and 153 down-regulated),including 3 MYB related genes (up-regulated, LOC103415449, LOC103421948, LOC103432338) and 2 bHLH genes(up-regulated, LOC103436250, LOC103437863) between striped and blushed apple.At the color turning period, there were 48 DAMs,including 20 flavonoids, 880 DEGs (274 up-regulated and 606 down-regulated), including 3 differentially expressed E2.3.1.133, HCT genes(down-regulated), 2 differentially expressed F3H genes (down-regulated), 1 differentially expressed BZ1 gene (down-regulated) and 2 differentially expressed ANS genes (up-regulated) and 2 up-regulated MYB related genes (LOC103411576, LOC103412495), 5 down-regulated MYB related genes(LOC103400953, LOC103408672, LOC103415404, LOC103420697, LOC103421948), 1 differentially expressed bHLH gene(down-regulated, LOC103400870). At the complete coloring period，there were 95 DAMs,including 34 flavonoids, 2258 DEGs (1159 up- and 1099 down-regulated), including 3 differentially expressed E2.3.1.133, HCT genes(down-regulated), 1 differentially expressed E2.3.1.133, HCT genes(up-regulated), 2 differentially expressed CYP98A genes (up-regulated), 4 differentially expressed CHS genes (up-regulated), 2 differentially expressed E5.5.1.6 genes(up-regulated), 2 differentially expressed CYP75B1 genes (up-regulated), 2 differentially expressed F3R genes (up-regulated), 2 differentially expressed ANS genes (up-regulated), 1 differentially expressed DFR genes (up-regulated), 2 differentially expressed BZ1 genes (up-regulated) and 1 differentially expressed MYB related gene (up-regulated, LOC103401575) .There were both 10 kinds of cyanidin in apple peel at color turning period and complete coloring period, Keracyanin and Cyanin were up-regulated at color turning period and Cyanidin-3-O-(6''-O-malonyl)glucoside was up-regulated at complete coloring period.Conclusions: Our researches provide important information on the anthocyanin metabolites and the candidate genes involved in the anthocyanin biosynthesis pathways of Fuji apple in M.domestcia.

Transcriptomics Reveals the ERF2-bHLH2-CML5 Module Responses to H2S and ROS in Postharvest Calcium Deficiency Apples

Calcium deficiency usually causes accelerated quality deterioration in postharvest fruit, whereas the underlining mechanism is still unclear. Here, we report that calcium deficiency induced the development of bitter pit on the surface of apple peels compared with the healthy appearance in control apples during postharvest storage. Physiological analysis indicates that calcium-deficient peels contained higher levels of superoxide anion (O2•−), malondialdehyde (MDA), total phenol, flavonoid contents and polyphenol oxidase (PPO) activity, and reduced calcium, H2S production, anthocyanin, soluble protein content, and peroxidase (POD) activity compared with those in calcium-sufficient peels. The principal component analysis (PCA) results show that calcium content, ROS, and H2S production were the main factors between calcium-deficient and calcium-sufficient apple peels. Transcriptome data indicated that four calmodulin-like proteins (CMLs), seven AP2/ERFs, and three bHLHs transcripts were significantly differentially expressed in calcium-deficient apple peels. RT-qPCR and correlation analyses further revealed that CML5 expression was significantly positively correlated with the expression of ERF2/17, bHLH2, and H2S production related genes. In addition, transcriptional co-activation of CML5 by ERF2 and bHLH2 was demonstrated by apple transient expression assays and dual-luciferase reporter system experiments. Therefore, these findings provide a basis for studying the molecular mechanism of postharvest quality decline in calcium-deficient apples and the potential interaction between Ca2+ and endogenous H2S.

Production and characterization of acetic fermentation with different fruit peels

Acetic fermentation or vinegar is the product obtained from fermented alcoholic wort, cereals or hydroalcoholic mixture with a minimum volatile acidity of 4g/100m.L-1. The present study produced, characterized and correlated the total dry extract with the density of the acetic fermented produced from the pineapple and apple peels. The fermentation process used pineapple and apple peel with culture medium, 10% hydroalcoholic solution, room temperature between 28 ± 2°C and irrigation 4 (four) times a day, without aeration for 12 days. Physico-chemical determinations of volatile acidity, density, dry extract, pH and alcohol content at 20°C were performed. The ANOVA variance analysis and the 5% Tukey test identified a difference between the analyzed acetic fermented. The acetic fermentations analyzed showed results within the established by Brazilian legislation. The relationship between the physical-chemical variables and the acetic fermented was studied by Principal Component Analysis (PCA). It was obtained that, with 5 components, more than 97.9% of the variability of the data were explained. There was a significant correlation between dry extract and vinegar density. The acetic fermented produced have similar physical-chemical characteristics to those produced industrially, which makes them suitable for consumption as commercial vinegars.

Physico-Chemical Properties of Biscuits Enriched with Dried Microwave-Blanched Fruit Peelings

Aims: To investigate the dough rheological properties as well as physical, nutritional, antioxidant and sensory properties of biscuits supplemented with dried microwave-blanched orange, apple and pomegranate peels at various levels (0-10%, wheat flour substitution). Methodology: Water absorption capacity and pasting properties of wheat flour blended with fruit peels were assessed using farinograph and micro viscoamylograph. Physico-chemical properties as well as antioxidant activities were measured using standard methods. The sensory analysis was performed by trained panelists. Results: Water absorption capacity of the dough increased significantly with increasing levels of orange and apple peels while it decreased with pomegranate peels. However, peak, hot paste, cold paste and breakdown viscosities of the dough significantly decreased with increasing proportions of apple and orange peels while they increased with pomegranate peels. The breaking force and weight of the biscuits supplemented with pomegranate peels were the lowest. Supplementation of biscuits with fruit peelings enhanced the ash and fibre content of the biscuits but had no significant effect on their antioxidant activities except for biscuits containing 10% apple peels which had higher antioxidant activity compared to biscuit controls. Biscuits supplemented with 5% of fruit peels were the most appreciated in terms of surface character, crumb colour and texture. Conclusion: This study showed that dried microwave-blanched apple peels can be incorporated into biscuits to enhance both their nutritional and antioxidant properties.

Identification, Comparison and Classification of Volatile Compounds in Peels of 40 Apple Cultivars by HS–SPME with GC–MS

Aroma is an important quality indicator for apples and has a great influence on the overall flavour and consumer acceptance. However, the information of the aroma volatile compounds in apple peels is largely unknown. In this study, evaluation of volatile compounds in peels of 40 apple cultivars was carried out using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). A total of 78 volatile compounds were identified, including 47 esters, 12 aldehydes, 5 alcohols, 3 ketones, 1 acid and 10 others. Eight volatile compounds were common in all apple cultivars. Cultivar Changfu No. 2 contained the highest number of volatile compounds (47), while Qinyue contained the least (20). Honey Crisps had the highest volatile content, at 27,813.56 ± 2310.07 µg/kg FW, while Huashuo had the lowest volatile content, at 2041.27 ± 120.36 µg/kg FW. Principal component analysis (PCA) clustered the 40 apple cultivars into five groups. Aroma is cultivar-specific, volatile compounds of hexyl butyrate, hexyl 2-methylbutyrate and hexyl hexanoate, together with hexanal, (E)-2-hexenal, 1-hexanol, estragole and α-farnesene could be proposed for apple cultivar classification in the future.

Valorization of Apple Peels through the Study of the Effects on the Amyloid Aggregation Process of κ-Casein

Waste valorization represents one of the main social challenges when promoting a circular economy and environmental sustainability. Here, we evaluated the effect of the polyphenols extracted from apple peels, normally disposed of as waste, on the amyloid aggregation process of κ-casein from bovine milk, a well-used amyloidogenic model system. The effect of the apple peel extract on protein aggregation was examined using a thioflavin T fluorescence assay, Congo red binding assay, circular dichroism, light scattering, and atomic force microscopy. We found that the phenolic extract from the peel of apples of the cultivar “Fuji”, cultivated in Sicily (Caltavuturo, Italy), inhibited κ-casein fibril formation in a dose-dependent way. In particular, we found that the extract significantly reduced the protein aggregation rate and inhibited the secondary structure reorganization that accompanies κ-casein amyloid formation. Protein-aggregated species resulting from the incubation of κ-casein in the presence of polyphenols under amyloid aggregation conditions were reduced in number and different in morphology.