Nutritious, balanced, tasty and easy to eat, fruit is an indispensable health food for consumers. With consumers\' increasing respect for the concept of health, green and nutrition, the peel, which has higher nutritional value compared to the pulp, is gradually being emphasized in the consumption process. The suitability of fruit peels for consumption is influenced by various factors, such as the amount of pesticide residues, nutrient content, ease of peeling, and fruit texture, but there is a lack of relevant studies to guide consumers\' scientific intake of fruit peels. This review first investigated chineses consumers consumption of common fruits with peels, especially eight fruits that are controversial in terms of whether to consume them with peels, and the results showed that whether people consume peels depends mainly on their nutritional value and pesticide residues. Based on this, the paper discusses the common methods of pesticide detection and removal from fruit peels, as well as the nutrients contained in different fruit peels and their physiological activities, if the peels usually have stronger antioxidant, anti-inflammatory and anti-tumor activities than the pulp. Finally, reasonable dietary recommendations are made on whether fruits should be consumed with their peels, with a view to guiding chineses consumers towards scientific consumption and provide theoretical basis for relevant research in other countries.

To evaluate the release and activity of Indian jujube phenolics in vivo, its peel and pulp were subjected to simulated digestions. The phenolics content and antioxidant activity of the digested samples were determined. The results showed that the total phenolics/flavonoids in the peel were respectively 4.63 and 4.48 times higher than that in the pulp. The release of phenolics and flavonoids respectively increased by 79.75% and 39.98% in the peel and 86.34% and 23.54% in the pulp after the intestinal digestion. The correlation between the total phenolics/flavonoids and antioxidant activity was higher in the peel (r > 0.858, p < 0.01) than that in the pulp. The phenolics profiles of the peel were almost the same after the digestion, and four phenolics including naringenin tri-glycoside, quercetin-3-O-[(2-hexosyl)-6-rhamnosyl] -hexoside, quercetin-3-O-pentosylhexoside and quercetin-3-O-(2-pentosyl -rhamnoside)-4\'-O-rhamnoside were found to be the main flavonoids of Indian jujube peel, and they showed high recovery (>89.88%) during the digestion, implying that these phenolics may play a vital role in the function of Indian jujubes.

Pyrus ussuriensis (Maxim.) is a unique pear tree that grows in northern China. The tree has strong cold resistance and can withstand low temperatures from -30 °C to -35 °C. Due to its unique growth environment, its fruit is rich in minerals and has much higher levels of minerals such as K, Ca and Mg than the fruit of Pyrus pyrifolia (Nakai.) and Pyrus bretschneideri (Rehd.) on the market, and many say the ripe fruit tastes better than other varieties. A comprehensive analysis of the characteristics of mineral elements in the fruits of different varieties of P. ussuriensis will provide a valuable scientific basis for the selection, breeding and production of consumer varieties of P. ussuriensis, and provide a more complete understanding of nutritional differences between fruit varieties.
In this study, 70 varieties of wild, domesticated and cultivated species of P. ussuriensis from different geographical locations were compared. Targeting four main mineral elements and eight trace mineral elements contained in the fruit, the differences in mineral content in the peel and pulp of different varieties of P. ussuriensis were analyzed, compared and classified using modern microwave digestion ICP-MS.
The mineral elements in the fruit of P. ussuriensis generally followed the following content pattern: K > P > Ca > Mg > Na > Al > Fe > Zn > Cu > Cr > Pb > Cd. The mineral element compositions in the peel and pulp of different fruits were also significantly different. The four main mineral elements in the peel were K > Ca > P > Mg, and K > P > Mg > Ca in the pulp. The mineral element content of wild fruit varieties was higher than that of cultivated and domesticated varieties. Correlation analysis results showed that there was a significant positive correlation between K, P and Cu in both the peel and pulp of P. ussuriensis fruit (P < 0. 01). Cluster analysis results showed that the 70 varieties of P. ussuriensis could be divided into three slightly different categories according to the content of the peel or pulp. According to the contents of the fruit peel, these varieties were divided into: (1) varieties with high Na, Mg, P, K, Fe and Zn content, (2) varieties with high Ca content and (3) varieties with medium levels of mineral elements. According to the fruit pulp content, these varieties were divided into: (1) varieties with high Mg, P and K content, (2) varieties with low mineral element content, and (3) varieties with high Na and Ca content. The comprehensive analysis of relevant mineral element content factors showed that \'SSHMSL,\' \'QYL,\' \'SWSL\' and \'ZLTSL-3\' were the best varieties, and could be used as the focus varieties of future breeding programs for large-scale pear production.

Citrus is an important genus in the Rutaceae family, with high medicinal and economic value, and includes important crops such as lemons, orange, grapefruits, limes, etc. The Citrus species is rich sources of carbohydrates, vitamins, dietary fibre, and phytochemicals, mainly including limonoids, flavonoids, terpenes, and carotenoids. Citrus essential oils (EOs) consist of several biologically active compounds mainly belonging to the monoterpenes and sesquiterpenes classes. These compounds have demonstrated several health-promoting properties such as antimicrobial, antioxidant, anti-inflammatory, and anti-cancer properties. Citrus EOs are obtained mainly from peels, but also from leaves and flowers, and are widely used as flavouring ingredients in food, cosmetics, and pharmaceutical products. This review focused on the composition and biological properties of the EOs of Citrus medica L. and Citrus clementina Hort. Ex Tan and their main constituents, limonene, γ-terpinene, myrcene, linalool, and sabinene. The potential applications in the food industry have been also described. All the articles available in English or with an abstract in English were extracted from different databases such as PubMed, SciFinder, Google Scholar, Web of Science, Scopus, and Science Direct.

The kiwi berry (Actinidia arguta) has been widely studied because of its rich phenolic, flavonoid, and vitamin C contents. Numerous reports have demonstrated that fruit peels contain higher phenolic content and antioxidant activity than that of flesh. In this study, the phytochemical content and antioxidant activities of peel and flesh extracts of six kiwi berries were analyzed from four regions (namely, Dandong, Benxi, Taian, and Tonghua) in China. The antioxidant activity was determined using the peroxyl radical scavenging capacity (PSC) and cellular antioxidant activity (CAA) assays. The phenolic, flavonoid, and vitamin C contents of kiwi berry peel were 10.77, 13.09, and 10.38 times richer than that of kiwi berry flesh, respectively. In addition, the PSC and CAA values of kiwi berry peel were higher than those of kiwi berry flesh. The analysis of the separation and contents of phenolics were performed by the high-performance liquid chromatography (HPLC)-diode-array detectormass spectrometry/mass (DAD-MS/MS) system, and the results illustrated that protocatechuic acid, caffeic acid, chlorogenic acid, and quinic acid were the major phenolic compounds. In conclusion, this study indicated that kiwi berry peel contains a rich source of antioxidants. These data are of great significance for the full development and utilization of kiwi berries in these four regions of China to produce nutraceutical and functional foods.

Akebia trifoliata is a fruit with rich nutritional properties, and its peel is produced as a by-product. In this research, we investigated the influences of microwave-assisted extraction parameters on antioxidant activity of the extract from Akebia trifoliata peels, and the ferric-reducing antioxidant power (FRAP) and Trolox equivalent antioxidant capacity (TEAC) as well as total phenolic contents (TPC) were used to optimize extraction parameters. The influences of ethanol concentration, microwave power and solvent-to-material ratio, as well as extraction temperature and time on TPC, FRAP and TEAC values, were assessed using single-factor tests. Three parameters with obvious effects on antioxidant capacity were selected to further investigate their interactions by response surface methodology. The optimal extraction parameters of natural antioxidants from Akebia trifoliata peels were ethanol concentration, 49.61% (v/v); solvent-to-material ratio, 32.59:1 mL/g; extraction time, 39.31 min; microwave power, 500 W; and extraction temperature, 50 °C. Under optimal conditions, the FRAP, TEAC and TPC values of Akebia trifoliata peel extracts were 351.86 ± 9.47 µM Fe(II)/g dry weight (DW), 191.12 ± 3.53 µM Trolox/g DW and 32.67 ± 0.90 mg gallic acid equivalent (GAE)/g DW, respectively. Furthermore, the main bioactive compounds (chlorogenic acid, rutin and ellagic acid) in the extract were determined by high-performance liquid chromatography. The results are useful for the full utilization of the by-product from Akebia trifoliate fruit.

Banana (Musa cavendish) is one of the most popular fruits globally and is an important foodstuff in many regions, attributed to its high nutritional value. Contrast to its high consumption volume, relatively little research has been conducted on banana lipidome. In this study, two classic lipid extraction methods, Folch and Bligh-Dyer, were compared for studying the banana lipidome in both the peel and pulp by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Lipidomic profiles were also investigated to understand the changes of lipid molecules during three ripening stages (unripe, ripe, and overripe), and differences in lipids from different origins were also compared. This study suggested that although both Folch and Bligh-Dyer methods allow lipidome investigation, the latter demonstrated advantage in rendering higher extraction efficiency for the majority of lipid molecules in banana samples, particularly in the pulp. In peel, there were differences in the trends of each lipid classes at various stages of maturity, while the majority of lipid classes in pulp reached the highest levels with reduced desaturation at ripe stage, consistent with previous studies. Moreover, the lipidomic profiles of bananas in different habitats differed significantly according to partial least-squares discriminant analysis. This study for the first time provided comprehensive atlas of lipidomic changes of Musa cavendish during maturity and in different origins. These findings will facilitate better understanding of biochemical changes in banana and offer new tools for food chemical analyses in the understanding of mechanisms underlying lipid metabolism.

Grapes are widely used in the wine and juice industries, which can lead to massive amounts of waste, mostly grape peels and seeds. The antioxidant capacities, total phenolic and flavonoid contents and phenolic profiles of peels and seeds from 30 grape varieties were systemically assessed. The antioxidant activities of fat-soluble, water-soluble and insoluble-bound fractions of grape peels and seeds were evaluated using ferric-reducing antioxidant power and Trolox equivalent antioxidant capacity assays, and their total phenolic contents and total flavonoid contents were determined by the Folin-Ciocalteu method and AlCl₃ colorimetry, respectively. It was found that the antioxidant capacities were diverse among different grape peels and seeds. Moreover, several phenolic compounds were identified and quantified, including gallic acid, cyanidin-3-glucoside, epicatechin, catechin gallate, ferulaic acid, rutin and resveratrol, which could contribute to the antioxidant capacities of these grape peels and seeds. Several grape wastes with strong antioxidant activity could be abundant sources of natural bioactive compounds, and have the potential for development into functional foods, food additives and pharmaceuticals.

Green banana fruit is an important starch resource that consists of flesh and peel. The physicochemical properties of flesh starch have been widely studied; however, those of peel starch have hardly been studied, leading to the waste of peel. In this study, the physicochemical properties of the starches from the flesh and peel of green banana fruit were investigated and compared. The dry flesh and peel had 69.5% and 22.6% starch content, respectively. The starch had oval and irregular granules with eccentric hila. Their starches had similar bimodal size distribution; the volume-weighted mean diameter was approximate 17 μm, and the peel starch had a slightly smaller granule size than the flesh starch. The maximum absorption wavelength was higher in peel starch than in flesh starch. The apparent amylose content of flesh and peel starch was 21.3% and 25.7%, respectively. The flesh and peel starches both exhibited B-type crystalline structures and had similar relative crystallinity, short-range ordered degrees, and lamellar structures. The swelling power was similar between flesh and peel starches, but the water solubility was higher in peel starch than in flesh starch at 95 °C. The peel starch had a higher gelatinization temperature than flesh starch, but their gelatinization temperature range and enthalpy were similar. Both flesh and peel starches showed a diphasic hydrolysis dynamic, but peel starch had higher resistance to porcine pancreatic α-amylase hydrolysis than flesh starch. The contents of rapidly digestible starch, slowly digestible starch, and the resistant starch of flesh and peel were 1.7%, 4.3%, 94.1% and 1.4%, 3.4%, 95.2%, respectively, for native starch, and 73.0%, 5.1%, 21.9%, and 72.3%, 4.5%, 23.2%, respectively, for gelatinized starch.

Mandarin (Citrus reticulata), a non-climacteric fruit, is an economically important fruit worldwide. The mechanism underlying senescence of non-climacteric fruit is poorly understood. In this study, a gel-based proteomic study followed by LC-ESI-MS/MS analysis was carried out to investigate the proteomic changes involved in peel senescence in harvested mandarin \"Shatangju\" fruit stored for 18 days. Over the course of the storage period, the fruit gradually senesced, accompanied by a decreased respiration rate and increased chlorophyll degradation and disruption of membrane integrity. Sixty-three proteins spots that showed significant differences in abundance were identified. The up-regulated proteins were mainly associated with cell wall degradation, lipid degradation, protein degradation, senescence-related transcription factors, and transcription-related proteins. In contrast, most proteins associated with ATP synthesis and scavenging of reactive oxygen species were significantly down-regulated during peel senescence. Three thioredoxin proteins and three Ca(2+) signaling-related proteins were significantly up-regulated during peel senescence. It is suggested that mandarin peel senescence is associated with energy supply efficiency, decreased antioxidant capability, and increased protein and lipid degradation. In addition, activation of Ca(2+) signaling and transcription factors might be involved in cell wall degradation and primary or secondary metabolism.