Apple Flavor Research Articles

Understanding consumer perception of a new product including apple pomace: The role of health, sustainability, and culinary engagement

The aim of the present study was to determine perception of a new product made with apple pomace including consumers from three different gastronomy cultures: Spain (Mediterranean), Poland (Central Europe), and Denmark (Nordic). The new product was mainly made from potato and apple pomace and had the typical texture of a savory snack (crisp-like), but it was characterized by its apple/sweet taste. Besides consumers from the aforementioned countries, a group of Foodies-consumers from 20 different nationalities participated in the study to determine potential differences on the product perception due to their high culinary knowledge/ingredients exposure. Over 600 consumers participated in the study. To segments consumers into different groups beyond nationality, the demographic questionnaire included the short version of the Food Choice Questionnaire, the Food Neophobia Scale, and questions on Dietary and Sustainability related habits. The hedonic response, as well as the intrinsic properties of the product (sweetness, sourness, saltiness, apple flavor, hardness, and crunchiness) were measured using Just-About-Right scales. Additional questions included assessment on the storytelling of the product, potential applications/consumption moments, and finally, the impact of adding a health (high in fiber) or a sustainable (made using by-products) claim. Analysis revealed variations in demographics across consumer groups, potentially influencing their perception of the new product. Including the question on applications/consumption moments of the new food, as well as gathering free words about the main aspects consumers valued about the food, were useful to better understand its potential in the market and design a proper communication strategy.

Lactic acid bacteria sequential fermentation improves viable counts and quality of fermented apple juice via generating two logarithmic phases

This study investigated the impact of lactic acid bacteria (LAB) sequential fermentation on viable counts and apple juice quality. The optimal fermentation conditions were obtained by a step-by-step optimization process, including pH 4.5, temperature 37 °C, the second inoculation time 16 h, total fermentation time 40 h and fermentation sequence (first 21,805 + 21,828, second 20,241). Under the optimal conditions, sequential fermentation allowed LAB to experience two logarithmic phases, increasing viable counts to 1.38 × 108 CFU/mL, exceeding simultaneous fermentation for 24 h and 40 h by 4.10 × 107 CFU/mL and 5.40 × 107 CFU/mL, respectively. This process enhanced sugar utilization, yielding more lactic acid and polyphenols. Furthermore, sequential fermentation improved DPPH (71.71 %) and ABTS (84.79 %) scavenging rates, and enriched volatile compounds, particularly beta-Damascenone, potentially contributing to floral and richer apple flavor. Sequential fermentation also achieved optimal sensory acceptability. This study proposes a novel strategy for high-density LAB fermentation to produce high-quality apple juice.

Characterization of Changes in Ripening Process of Volatile Apple Compounds Based on HS-SPME-GC-MS Analysis

The aim of this study was to identify the aromatic compounds present in different apple varieties and to gain insights into the changes in the aromatic compounds during ripening. Three apple varieties (“Red Astrachan”, “Ning Qiu”, and “Golden Delicious”) at different stages of ripening were selected for this study; their peel and pulp were analyzed via headspace solid-phase microextraction (HS-SPME)–gas chromatography–mass spectrometry (HS-SPME-GC-MS), and 30 volatile compounds were identified. The samples’ differences were analyzed using heat map cluster analysis, principal component analysis (PCA), and an independent samples t-test. The results showed that the content of aromatic compounds in the peel was higher than that in the pulp. The relative content of esters in the aromatic compounds of the three apple varieties followed the order of pulp > peel and “Ning Qiu” > “Golden Delicious” > “Red Astrachan”. This suggests that “Ning Qiu” combines the advantages of its parents in terms of its aroma content. The highest concentrations of aroma compounds in “Red Astrachan” and “Ning Qiu” accumulate before the ripening stage, and care should be taken to choose an appropriate harvesting time according to the different needs during production. The main compounds of “Red Astrachan” are aldehydes and C8 esters, while those of “Ning Qiu” and “Golden Delicious” are alkenes and esters. After analyzing the relative odor activity values (rOAVs) of key volatile compounds and their aroma descriptors during the harvest period, acetic acid pentyl ester, butanoic acid hexyl ester, hexanoic acid hexyl ester, and 2-ethyl-1-Hexanol were found to contribute the most to the overall flavor of the peel and pulp. “Ning Qiu” combines the parental advantages of the concentrated peel of “Red Astrachan” and the astringent pulp of “Golden Delicious”, with compounds in its composition that give a pleasing aroma. Mature “Ning Qiu” fruits have a more intense aroma and fruity flavor. The development of flavor-specific varieties has provided the theoretical basis for future research in molecular hybridization, molecular-assisted breeding, and the molecular biology of apple flavor synthesis and metabolism.

Practical 1-Methylcyclopropene Technology for Increasing Apple (Malus domestica Borkh) Storability in the Aksu Region.

In recent years, Aksu apple has become popular with consumers because of its unique texture and taste. At present, maintaining quality during storage is the key problem with the apples in the Aksu region. 1-Methylcyclopropene (1-MCP) can delay fruit senescence, so is widely used in fruit preservation. However, many factors affect the preservation effect of 1-MCP. The effects of 1-MCP concentration (0 µL·L-1, 1 µL·L-1, 3 µL·L-1, 5 µL·L-1, and 8 µL·L-1) and postharvest application time (0, 1 and 2 d after harvest) on the quality of stored apple were studied. It was found that 1 µL·L-1 1-MCP was more beneficial in improving the quality of stored apples, reduced the respiration intensity and decay rate, increased the fruit firmness and total soluble solid content, and reduced the relative content of ester volatile aroma components. In addition, 1-MCP treatment applied at different postharvest times also affected the sensory quality and flavor of apples. The effect of 1-MCP treatment immediately after harvest was better.

Analysis of Aroma Characteristics of 'Binzi' and 'Xiangguo' Apple-Ancient Cultivars in China.

'Binzi' (BZ) (Malus domestica subsp. chinensis var. binzi Li Y.N.) and 'Xiangguo' (XG) (Malus domestica subsp. chinensis var. xiangguo Li Y.N.) are the ancient cultivars in China. The BZ fruits have a low-fragrant flavor on harvest day but a high-fragrant flavor after storage at room temperature, while the XG fruits have a stronger flavor when mature. 'Starking' (SK) and 'Golden Delicious' (GD) fruits have a rich flavor and are recognized by all countries in the world. However, information on the differences between ancient Chinese cultivars and Western apple cultivars in aroma compounds remains unknown. The apple fruits were collected for continuous two years. Aroma compounds in the skin and pulp of the fruits were detected at room temperature (20 ± 1 °C) during storage. The dynamics of VOCs in BZ and SK fruits were more similarly reflected in esters, while those of XG and GD fruits were reflected in aldehydes and alcohols. Ethyl 2-methylbutyrate, with an extremely low odor threshold, was the main source of typical apple flavor in SK, BZ, and XG fruits, while hexyl acetate was the source of the banana flavor in GD fruits. 6-methyl-5-hepten-2-one and β-damascenone were the important ketones produced in the later stage of storage, derived from the carotenoid metabolism pathway and providing a citrus and rose flavor to the four apple cultivars. SK had the highest number of characteristic aroma components, which were mainly derived from the amino acid metabolism pathway, providing fruits with a sweet and fruity flavor. Although the characteristic aroma components of GD were derived from the fatty acid metabolic pathway, the number of volatile esters was lower. Ethyl butyrate, derived from the saturated fatty acid metabolism, had the highest content in BZ, providing a pineapple flavor; the flavor of XG was mainly derived from ethyl 2-methylbutyrate, 6-methyl-5-hepten-2-one, and β-damascenone. Therefore, we suggest BZ and XG apples as the aroma-breeding material with which to enrich new cultivars' aroma components, derived from the fatty acid metabolism and carotenoid metabolism pathways, respectively.

The relative importance of postharvest eating quality and sustainability attributes for apple fruit: A case study using new sensory–consumer approaches

Consumer-sensory methods based on check-all-that-apply (CATA) for texture and flavour terms and conceptual descriptors offer alternatives for characterising eating quality. In this study, ‘Red Delicious’, ‘Gala’ and ‘Scilate’ apples (Malus domestica Borkh.), which were of comparable instrumental firmness, and similar in crispness and apple flavour, evoked profoundly different consumer responses. Mean liking scores from 122 consumers were 7.1 (∼like moderately), 5.8 (∼like slightly), and 5.1 (∼neither like nor dislike) for ‘Scilate’, ‘Gala’, and ‘Red Delicious’ respectively, and cluster analysis indicated three consumer-segments: one that preferred ‘Scilate’ over the other cultivars (62 % of consumers), another that liked ‘Scilate’ and ‘Gala’ equally over ‘Red Delicious’ (26 %), and a small third segment that liked ‘Red Delicious’ and ‘Gala’ equally over ‘Scilate’ (12 %). In the associated experimental auction, consumers were provided with $US3, and the mean bids for ‘Scilate’, ‘Gala’, and ‘Red Delicious’ reflected the pattern of consumer liking at $US1.72, $US0.79, and $US0.52, respectively. Correspondence analysis plots of CATA data indicated that ‘Scilate’ was associated with sensory descriptors sweet, fruity, tropical and pear flavours and positive conceptual descriptors including exciting, complex, unique, premium, yummy, intense, and powerful. ‘Gala’ and ‘Red Delicious’ were associated with sensory descriptors including old, mealy, bland, green-grassy and sour-acidic and negative conceptual descriptors dissatisfied, inferior, boring, disappointing, and uninspiring. A best-worst scaling methodology was used to elicit consumers’ priorities regarding the aspects of apple quality and production sustainability. Despite the profound differences in eating quality uncovered in the hedonic and CATA tasks, the statement ‘tastes like the best apple eaten today’ was assessed as being only 23 % as important as the statement ‘grown in a way that is sustainable and does not harm the environment’ in consumer choices. This notable outcome was contradicted in a matching online study changing the eating quality statement ‘tastes like the best apple eaten today’ to ‘Crisp, juicy and sweet’ (the attributes most frequently identified in the sensory CATA). This suggests that trade-offs between eating quality and sustainability are subject to context effects associated with whether taste is an experienced or imagined factor. There is an urgent need to better understand how consumers’ needs for sustainability in the food production system might alter what is acceptable in terms of eating quality.

Assessment of a new apple flavour modular protein oral nutritional supplement

Assessment of a new apple flavour modular protein oral nutritional supplement

Evaluating the Non-Invasive Measurement of Apple Aroma Using Electronic Nose Device through Comparison with Direct Mass Spectrometry, Sugar Content, and Ripeness Measurements.

To compare apple aroma intensities, apples were analyzed from the calyx side (on the opposite side of the stem) using an electronic nose (e-nose) sensor device and direct mass spectrometry. The results indicated that the sensor value tended to increase in accordance with the total intensity of apple aroma components measured by direct mass spectrometry. In addition, the e-nose sensor values for apple aroma did not correlate with the sugar content and ripeness measurements using optical sensors. Moreover, the relative standard deviations of repeatability and intermediate precision in the measurement of apple flavor (apple lip balm) were within 1.36-9.96%. Similar to the utilization of sugar content and ripeness values, the aroma measured from the calyx side can be potentially used for apple evaluation.

Nutritional Composition of Some Selected Commercial Juice Made in Nigeria

Introduction: Nutrient-fortified food play a crucial role in addressing nutritional deficiencies among infants and children, making them more appealing for consumption. Research focuses on baby foods, particularly reconstituted juice drink, which serve as significant sources of essential minerals and vitamins. However, the nutrient composition of these products varies, leading to differences in quality. The objective of this study is to assess the disparities in the nutritional content of various children's juice drink available in the Nigerian market. Methods: Proximate analysis was carried out according to the standard procedure of Association of Official Analytical Chemists (AOAC) to evaluate the nutritional composition of the selected juice drink. Minerals content were determined using Atomic Absorption and Flame Spectroscopy Techniques. The determination of the Vitamin A content in the samples was conducted following a modified Spectrophotometric Method. For Ascorbic Acid (Vitamin C), the Vitamin C content in the samples was assessed utilizing a Spectrometric Method coupled with 2,4 Dinitrophenyl hydrazine (DNPH) procedures. Results: Examination of the proximate and mineral analyses of ten chosen fruit juice brands revealed notable variations. Capri sonne exhibited the highest moisture content at 94.2%, while Hollandia Yogurt has the lowest at 81.3%. Chapman, Nutri Milk, and Viju Apple Flavor Milk shared the highest ash content at 0.5%, whereas Hollandia Malt, Piko Orange, and Piko Strawberry displayed the lowest at 0.01%. Nestle Malt boasted the highest crude protein concentration at 4.38%, with Capri sonne recorded the lowest at 0.18%. Hollandia Yogurt and Hollandia Malt demonstrated the highest crude fiber content, while Vitavite Multivi, Piko Orange, and Piko Strawberry showed the lowest. Regarding total carbohydrates, Hollandia Yogurt topped the list at 14.6%, while Vitavite Multivi ranked lowest at 6.57%. Nestle Millo contained the highest vitamin C content at 25.7%, whereas Piko Strawberry has the lowest at 3.82%. Caprosonne registered the highest vitamin A content at 0.6%. In terms of mineral analysis, Hollandia Yogurt exhibited the highest sodium percentage at 22.6mg/g, while Nestle led in calcium, iron, and magnesium content at 120.4mg/g, 1.7mg/g, and 25.5mg/g, respectively. It can therefore be inferred from the outcome of this study that, Milo Nestle is the best drink for children due to its higher protein, carbohydrate, vitamins (A and C) and minerals (Ca, Mg, Fe, Na) contents, followed by Hollandia Malt as compared to other juice studied.

Identification of aroma compounds responsible for apple flavor via palatability score prediction in tree-based regression models

Apple flavor has been linked to the composition of aroma compounds; however, the impact of varying concentrations of aroma compounds remains poorly understood. While sensory evaluation is commonly used to analyze food palatability, assessing the effect of concentration of all aroma compounds poses challenges. This study screened 174 apple genotypes for significant aroma compounds using regression models, Gas chromatography–mass spectroscopy analysis, and sensory palatability scores. Two models viz. Random Forest and XGBoost were employed to predict palatability scores, surpassing the limitations of correlation analysis. Shapley's additive explanatory value analysis identified 5-hexenol, ethyl 2-methyl butyrate, 2-methylbutyl acetate, (E,E)-α-farnesene, and (Z)-3-hexenol as key aroma compounds. In a sensory evaluation validating the effect of aroma compound concentration, the variation in (E,E)-α-farnesene concentration negatively affected sensory palatability scores. This study demonstrated a novel approach for identifying aroma compounds that impact apple flavor, providing valuable insights to enhance apple quality and palatability.

Profiling apple volatile organic compounds in a New Zealand collection of germplasm as a resource for breeding cultivars with desirable flavors

Flavor is a major component of the apple eating experience, along with taste, texture and appearance. Apples produce a wide array of volatile organic compounds that impart particular flavors. Cultivars producing increased or novel flavors may have more desirability for consumers and help to differentiate the fruit. Efficiently breeding more flavorful apples requires understanding the volatiles present in apple germplasm and their potential sensory impact. As an initial step towards the development of more flavorful apple cultivars, a New Zealand collection of germplasm was surveyed, and seventy-three volatiles were identified as being present in at least half the accessions. Substantial differences in the presence and relative abundance of specific volatiles were uncovered across the accessions and could sometimes be linked to an apple’s flavor profile. The large number of volatiles analyzed allowed relationships between and among molecule classes to be established. Esters were found to be the main drivers of volatile differentiation across accessions. Apples tended to produce either ethyl or acetate esters, suggesting there is different genetic control for these two ester types. Additionally, esters generally had larger broad-sense heritabilities, indicating they could be easier targets for modifying apple flavor. This volatile dataset is a valuable resource for apple breeding, and increases the understanding of an important consumer trait.

Transcription factors MdMYC2 and MdMYB85 interact with ester aroma synthesis gene MdAAT1 in apple.

Volatile esters in apple (Malus domestica) fruit are the critical aroma components determining apple flavor quality. While the exact molecular regulatory mechanism remains unknown, jasmonic acid (JA) plays a crucial role in stimulating the synthesis of ester aromas in apples. In our study, we investigated the effects of methyl jasmonate (MeJA) on the production of ester aroma in apples. MeJA treatment significantly increased ester aroma synthesis, accompanied by the upregulation of several genes involved in the jasmonate pathway transduction. Specifically, expression of the gene MdMYC2, which encodes a transcription factor associated with the jasmonate pathway, and the R2R3-MYB transcription factor gene MdMYB85 increased upon MeJA treatment. Furthermore, the essential gene ALCOHOL ACYLTRANSFERASE 1 (MdAAT1), encoding an enzyme responsible for ester aroma synthesis, showed increased expression levels as well. Our investigation revealed that MdMYC2 and MdMYB85 directly interacted with the promoter region of MdAAT1, thereby enhancing its transcriptional activity. In addition, MdMYC2 and MdMYB85 directly bind their promoters and activate transcription. Notably, the interaction between MdMYC2 and MdMYB85 proteins further amplified the regulatory effect of MdMYB85 on MdMYC2 and MdAAT1, as well as that of MdMYC2 on MdMYB85 and MdAAT1. Collectively, our findings elucidate the role of the gene module consisting of MdMYC2, MdMYB85, and MdAAT1 in mediating the effects of JA and promoting ester aroma synthesis in apples.

Acute effects of flavored Black and mild cigars among young adult cigarette smokers.

The U.S. Food and Drug Administration proposed new product standards that would ban characterizing flavors (other than tobacco) in cigars. To inform this regulatory action, we compared physiological effects, use behavior, and subjective effects of four popular cigar flavors in cigar-naïve young adult cigarette smokers. Across five laboratory visits, participants (n = 25) used and evaluated own brand (OB) cigarettes or Black & Mild cigars (original, wine, apple, and cream flavors). Linear mixed models tested differences in saliva nicotine, exhaled carbon monoxide (CO), heart rate (HR), blood pressure (BP), puff topography, and subjective effects (p < .05). Compared to all cigars, OB resulted in higher nicotine boost (953 vs. < 300 ng/ml) and lower CO boost (4 vs. 8-9 ppm). Nicotine boost for original cigars (283 ng/ml) was significantly higher than wine (190 ng/ml). All products significantly increased HR/BP relative to baseline, but across time wine and apple cigars were associated with significantly lower HR than OB and BP effects varied. Relative to OB, participants took approximately 0.5 s longer puffs for all cigars and took significantly larger puffs (+ 21%-24%) of original, wine, and apple cigars. OB was rated more positively than all cigars, which had similar subjective effects. Wine cigars were disliked most and were less effective in reducing tobacco abstinence symptoms than OB; cream cigars were harsher and had stronger flavor intensity than original. The consistency in toxicant exposure, use behavior, and subjective effects across cigar flavors, including original, highlights the need for product standards to interpret characterizing flavors subject to prohibition broadly. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Integrative analysis of metabolome and genome-wide transcriptome reveal the flavor changes in apple (Malus pumila Mill) after the novel acaricide cyflumetofen application

Pesticide residues were found to interfere the nutrition and flavor of fruits. Apple flavor changes after pesticides application was investigated based on metabolic dynamics and underlying regulatory networks. In this study, cyflumetofen (CYF) systematically affected the nutrition and flavor formation on apple (Malus pumila Mill). CYF alters nutritional composition, but not total content of soluble sugars and organic acids. Palatability-related amino acid content decreased around 15% in CYF-treated apple. The contents of esters and alcohols responsible for fragrance and flavor decreased by approximately 10% in CYF-treated apples compared with controls. Non-target metabolomic and transcriptomic analysis showed that CYF mainly affected amino acid-, organic acid-, polyphenol-, and lipid-metabolism related pathways, leading to altered nutritional and flavor characteristics. In conclusion, the results suggested that CYF affected the primary metabolism of apple, resulting in unpleasant changes in nutritional and flavor composition. This study provided new insight into the metabolic regulation of flavor after pesticides application.

Relationships between sensory properties and metabolomic profiles of different apple cultivars.

Flavor is a critical factor in apple quality. To better understand apple flavor, this study aimed to identify the relationships between sensory attributes and the chemical composition (volatiles and non-volatiles) of apples using a combined metabolomic and sensory evaluation. Sensory results showed the positive (apple, fruity, pineapple, sweetness, sourness) and negative (cucumber) flavor attributes of apples. A metabolomic analysis with statistical correlations revealed significant metabolites related to the flavor attributes of apples. Volatile esters (e.g., hexyl acetate and 2-methylbutyl acetate for apple and fruity notes) and non-volatile sugars and acids (total sugars, tartaric acid, and malic acid for balanced sweet and tart flavors) were associated with the apple flavor preferred by consumers. Some aldehydes and alcohols (e.g., (E)-2-nonenal) contributed to a negative hedonic perception (cucumber). The collected information demonstrated the roles of key chemical compounds in apple flavor quality, and may be applicable to quality control.

Brewing a Craft Belgian-Style Pale Ale Using Pichia kudriavzevii 4A as a Starter Culture.

There is an expanding market for beer of different flavors. This study aimed to prepare a craft Belgian-style pale ale with a non-Saccharomyces yeast. Pichia kudriavzevii 4A was used as a sole starter culture, and malted barley as the only substrate. The ingredients and brewing process were carefully monitored to ensure the quality and innocuousness of the beverage. During fermentation, the yeast consumed 89.7% of total sugars and produced 13.8% v/v of ethanol. The product was fermented and then aged for 8 days, adjusted to 5% v/v alcohol, and analyzed. There were no traces of mycotoxins, lead, arsenic, methanol, or microbiological contamination that would compromise consumer health. According to the physicochemical analysis, the final ethanol concentration (5.2% v/v) and other characteristics complied with national and international guidelines. The ethyl acetate and isoamyl alcohol present are known to confer sweet and fruity flavors. The sensory test defined the beverage as refreshing and as having an apple and pear flavor, a banana aroma, and a good level of bitterness. The judges preferred it over a commercial reference sample of Belgian-style pale ale made from S. cerevisiae. Hence, P. kudriavzevii 4A has the potential for use in the beer industry.

Genetic analysis and QTL mapping of aroma volatile compounds in the apple progeny 'Fuji' × 'Cripps Pink'.

Aroma is an essential trait for apple fruit quality, but the understanding of biochemical mechanisms underlying aroma formation is still limited. To better characterize and assess the genetic potential for improving aroma quality for breeding, many efforts have been paid to map quantitative trait loci (QTLs) using a saturated molecular linkage map. In the present study, aroma profiles in ripe fruit of F1 population between 'Fuji' and 'Cripps Pink' were evaluated by gas chromatography-mass spectrometry (GC-MS) over 2019 and 2020 years, and the genetics of volatile compounds were dissected. In total, 38 volatile compounds were identified in 'Fuji' × 'Cripps Pink' population, including 23 esters, 3 alcohols, 7 aldehydes and 5 others. With the combination of aroma phenotypic data and constructed genetic linkage map, 87 QTLs were detected for 15 volatile compounds on 14 linkage groups (LGs). Among them, a set of QTLs associated with ester production identified and confirmed on LG 6. A candidate gene MdAAT6 in the QTL mapping interval was detected. Over-expression of MdAAT6 in tomato and apple fruits showed significantly higher esters accumulation compared to the control, indicating it was critical for the ester production. Our results give light on the mode of inheritance of the apple volatilome and provide new insights for apple flavor improvement in the future.

Sensory quality and consumer perception of high pressure processed orange juice and apple juice

High pressure processing (HPP) is an alternative to thermal pasteurization (TP) of beverages that can impart an extended shelf-life while delivering products with “fresh-like” sensory properties. However, studies documenting the sensory changes associated with HPP of fruit juices and their relation to consumer preferences are limited. In this paper, the effect of HPP on sensory quality and consumer perception of orange- and apple juice was investigated using a full experimental design with samples varying in treatment (HPP, TP), storage time (0, 3, 11 weeks for orange juice and 0, 4, 12 weeks for apple juice) and storage temperature (4 °C, 25 °C). Samples were first analyzed by descriptive analysis with a trained panel and subsequently submitted to a consumer liking test (N = 75). Treatment and storage conditions had a significant impact on sensory quality and on consumer perception. HPP could better maintain the sensory quality of both juices. Cold storage was effective in maintaining the product quality over the entire storage period. The main drivers of consumer liking were attributes associated with shorter storage times and/or cold storage (e.g., intensity of orange aroma and flavor in orange juice, apple flavor and aftertaste in apple juice), and to a lesser extent to treatment.

Calcyclin-binding protein-promoted degradation of MdFRUCTOKINASE2 regulates sugar homeostasis in apple.

Fructokinase (FRK) activates fructose through phosphorylation, which sends the activated fructose into primary metabolism and regulates fructose signaling capabilities in plants. The apple (Malus × domestica) FRK gene MdFRK2 shows especially high affinity to fructose, and its overexpression decreases fructose levels in the leaves of young plants. However, in the current study of mature plants, fruits of transgenic apple trees overexpressing MdFRK2 accumulated a higher level of fructose than wild-type (WT) fruits (at both young and mature stages). Transgenic apple trees with high mRNA MdFRK2 expression showed no significant differences in MdFRK2 protein abundance or FRK enzyme activity compared to WT in mature leaves, young fruits, and mature fruits. Immunoprecipitation-mass spectrometry analysis identified an skp1, cullin, F-box (SCF) E3 ubiquitin ligase, calcyclin-binding protein (CacyBP), that interacted with MdFRK2. RNA-sequencing analysis provided evidence for ubiquitin-mediated post-transcriptional regulation of MdFRK2 protein for the maintenance of fructose homeostasis in mature leaves and fruits. Further analyses suggested an MdCacyBP-MdFRK2 regulatory module, in which MdCacyBP interacts with and ubiquitinates MdFRK2 to facilitate its degradation by the 26S proteasome, thus decreasing the FRK enzyme activity to elevate fructose concentration in transgenic apple trees. This result uncovered an important mechanism underlying plant fructose homeostasis in different organs through regulating the MdFRK2 protein level via ubiquitination and degradation. Our study provides usable data for the future improvement of apple flavor and expands our understanding of the molecular mechanisms underlying plant fructose content and signaling regulation.

Variations in volatile organic compounds in Zhenyuan Daocai samples at different storage durations evaluated using E-nose, E-tongue, gas chromatography, and spectrometry

In this study, the changes in volatile organic compounds (VOCs) in Zhenyuan Daocai at different storage durations were determined using electronic tongue (E-tongue), electronic nose (E-nose), and other methods. Gas chromatography-ion mobility spectrometry (GC-IMS) identified 81 VOCs in Zhenyuan Daocai, which originated either from the raw materials or developed during processing and storage. Isothiocyanates were the characteristic VOCs in the raw materials of Zhenyuan Daocai, imparting a mustard flavor, heptanal, nonanal, 1-hydroxy-2-propanone, and 2-pentylfuran were the compounds obtained after processing, imparting orange, sweet, and nutty flavors. The characteristic VOCs observed in Daocai after one year of storage were (E, E) −2,4-hexadienal, ethyl acetate, and isoamyl acetate, which contributed to the floral and fruity odors. The characteristic VOCs in Daocai after four years of storage were furfural, 2-methyl-3-furanthiol, and methyl butyrate, which contributed to the almond, roasted meat, fried coffee, and apple flavors.