Preharvest Application of Phenylalanine Induces Red Color in Mango and Apple Fruit's Skin

Gas chromatography-mass spectrometry metabolic profiling and sensory evaluation of greenhouse mangoes (Mangifera indica L. 'Irwin') over multiple harvest seasons

Compared to outdoor mango cultivation in the tropics, greenhouse cultivation in temperate regions is less reported due to its short history and small scale. Here, we evaluated for the first time the taste-focused quality of greenhouse-grown mangoes (Irwin) by GC-MS metabolic profiling and sensory evaluation for over three years (2021-2023). The relative standard deviation in sensory evaluation scores was approximately 15 % each year. Meanwhile, principal component analysis was performed on 45 identified metabolites and clustered with similar topology over three years. Orthogonal partial least squares regression analysis showed that a prediction model could be constructed with R2, Q2 = 0.9 or higher for all three years. Furthermore, the 2021 prediction model was used to evaluate the accuracy of sensory evaluation scores in a different year (2023). Compared to the model that used all 45 metabolites as explanatory variables, the accuracy of the model improved when using only 24 important metabolites which are common to both years (2021 and 2022), suggesting that these metabolites are highly reproducible across years. This study would contribute not only to fundamental greenhouse information, but also to the improvement of quality and cultivation methods in greenhouse in the future.

From White to Reddish-Brown: The Anthocyanin Journey in Stropharia rugosoannulata Driven by Auxin and Genetic Regulators

Stropharia rugosoannulata, or wine-cap Stropharia, is a well-known edible mushroom cultivated globally. The pileipellis color is a crucial quality attribute of S. rugosoannulata, exhibiting significant variation throughout its developmental stages. However, the pigment types and regulatory mechanisms behind color variation remain unclear. The metabolome analysis found that the anthocyanin biosynthesis pathway was significantly enriched and anthocyanins accumulated steadily in fruiting bodies during three developmental stages. The pileipellis pigment was extracted, and HPLC-MS confirmed the presence of anthocyanins. Notably, significant differences in anthocyanin content were observed among the various colored varieties. Thus, anthocyanins contribute to the pileipellis color of S. rugosoannulata. Through further investigation, this study elucidated, for the first time, the relationship between the "SrNFYA-SrDRF2" regulatory module and anthocyanin accumulation. Combined multiomics assays and HPLC analysis revealed that auxin functions as a signaling molecule that regulates the accumulation of anthocyanins in the pileipellis. Subsequently, the hub gene of anthranilate synthase for auxin synthesis was identified as SrTRP1, and the transcription factor SrMYB1 was verified as a regulator of SrTRP1, influencing auxin accumulation. These findings provide a valuable resource for the targeted enhancement of the quality of S. rugosoannulata.

Changes in Postharvest Quality and Physiological Attributes of Strawberry Fruits Influenced by l-Phenylalanine

Strawberry (Fragaria × ananassa) is a popular fruit with rich nutrients and a delicious taste. But this fruit is very vulnerable to diseases and decay. Therefore, l-phenylalanine (Phe) (0, 4, 8 mM) was considered to improve biochemical characteristics and activity of antioxidant enzymes in strawberry fruit cv. Sabrina under cold storage (5, 10, 15 days). After treatment and storage, traits including weight loss, total phenol (TP), antioxidant capacity, ascorbic acid, total anthocyanin (TA), total flavonoid (TF), malondialdehyde (MDA), soluble protein content and antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (POD) and phenylalanine ammonialyase (PAL) were evaluated at 5-day intervals. Our findings showed that the treatment of l-phenylalanine in different concentrations prevented the weight loss of the fruit compared to the control and maintained and increased TP, antioxidant capacity, ascorbic acid, TA, TF, soluble protein and SOD, CAT, APX, POD, and PAL enzymes activity. Also, Phe decreased the MDA content and peroxidation of lipid. The results showed that 4 mM Phe is the best treatment for improving phytochemical characteristics and maintaining fruit quality. The findings indicated that Phe treatment may be useful to improve quality and increase postharvest shelf life in strawberry fruits.

Preharvest spraying of phenylalanine activates the sucrose and respiratory metabolism in muskmelon wounds during healing

Phenylalanine (Phe) accelerates fruit wound healing by activating phenylpropanoid metabolism. However, whether Phe affects sucrose and respiratory metabolism in fruit during wound healing remains unknown. In this research, we found that preharvest Phe spray promoted sucrose degradation and increased glucose and fructose levels by activating acid invertase (AI), neutral invertase (NI), sucrose synthase (SS) and sucrose phosphate synthase (SPS) on harvested muskmelons. The spray also activated hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), malate dehydrogenase (MDH), succinate dehydrogenase (SDH) and glucose-6-phosphate dehydrogenase (G6PDH). In addition, the spray improved energy and reducing power levels in the fruit. Taken together, preharvest Phe spray can provide carbon skeleton, energy and reducing power for wound healing by activating the sucrose metabolism, Embden-Meyerhof-Parnas (EMP) pathway, tricarboxylic acid (TCA) cycle and pentose phosphate (PPP) pathway in muskmelon wounds during healing, which is expected to be developed as a new strategy to accelerate fruit wound healing.

Combination of Sodium Nitroprusside and Controlled Atmosphere Maintains Postharvest Quality of Chestnuts through Enhancement of Antioxidant Capacity

The purpose of this study was to clarify the effect of CA (controlled atmosphere, 2-3% O2 + 3% CO2) and NO (nitric oxide, generated by 0.4 nM sodium nitroprusside), alone or combined (CA + NO), on the physio-chemical properties, enzyme activities and antioxidant capacities of chestnuts during storage at 0 °C for 180 d. Compared with control (CT), CA and CA+NO both improved the storage quality of the samples, but only CA resulted in more ethanol production. Moreover, these improvements were further enhanced and ethanol synthesis was inhibited by the addition of NO. A spectrometer was used to assess the production of phenolic content (TPC) and activities of phenylalanine ammonia-lyase (PAL), superoxide dismutas (SOD), peroxidase (POD), catalase (CAT) and polyphenol oxidase (PPO) as influenced by CA or CA+NO treatments. Higher TPC, PAL, SOD, POD, CAT, and lower PPO were observed in CA alone, and more so in the combination with NO group. The increased antioxidant production and enhanced antioxidant activities contributed to scavenging reactive oxygen species (ROS) and reducing malondialdehyde (MDA). This study unveiled the correlations and differences between the effects of CA and CA+NO on storage quality, providing valuable insights into postharvest preservation and suggesting that the combination (CA+NO) was more beneficial for quality maintenance in chestnuts.

Phenylalanine in motion: A tale of an essential molecule with many faces

Phenylalanine has a unique role in plants as a source of a wide range of specialized metabolites, named phenylpropanoids that contribute to the adjustment of plants to changing developmental and environmental conditions. The profile of these metabolites differs between plants and plant organs. Some of the prominent phenylpropanoids include anthocyanins, phenolic acids, flavonoids, tannins, stilbenes, lignins, glucosinolates and benzenoid phenylpropanoid volatiles. Phenylalanine biosynthesis, leading to increased phenylpropanoid levels, is induced under stress. However, high availability of phenylalanine in plants under non-stressed conditions can be achieved either by genetically engineering plants to overproduce phenylalanine, or by external treatment of whole plants or detached plant organs with phenylalanine solutions. The objective of this review is to portray the many effects that increased phenylalanine availability has in plants under non-stressed conditions, focusing mainly on external applications. These applications include spraying and drenching whole plants with phenylalanine solutions, postharvest treatments by dipping fruit and cut flower stems, and addition of phenylalanine to cell suspensions. The results of these treatments include increased fragrance in flowers, increased aroma and pigmentation in fruit, increased production of health promoting metabolites in plant cell cultures, and increased resistance of plants, pre- and post-harvest, to a wide variety of pathogens. These effects suggest that plants can very efficiently uptake phenylalanine from their roots, leaves, flowers and fruits, translocate it from one organ to the other and between cell compartments, and metabolize it into phenylpropanoids. The mechanisms by which Phe treatment increases plant resistance to pathogens reveal new roles of phenylpropanoids in induction of genes related to the plant immune system. The simplicity of treatments with phenylalanine open many possibilities for industrial use. Many of the phenylalanine-treatment effects on increased resistance to plant pathogens have also been successful in commercial field trials.

Physicochemical Characteristics, Antioxidant Properties and Consumer Acceptance of Greek Yogurt Fortified with Apple Pomace Syrup

Despite having high polyphenolic phytochemicals and functional components, apple pomace (AP) is often discarded in landfills, leading to pollution. The study aimed to find a sustainable application for AP in Greek yogurt fortified with AP syrup (APS). Physicochemical characteristics and antioxidant properties were analyzed for APS (APS0.00, APS1.25, APS2.50, APS3.75, APS5.00). As the AP content in the syrup increased, moisture content, titratable acidity, and viscosity significantly increased (p < 0.05). The total polyphenols and flavonoid content of APS increased with increasing AP content. In Greek yogurt fortified with APS (APY), reducing sugar content (0.55 mg/mL to 0.71 mg/mL) significantly increased with fermentation time and AP content, whereas pH level (6.85 to 4.28) decreased. The antioxidant activities by DPPH radical scavenging activity, ABTS radical scavenging activity, ferric reducing antioxidant power, and reducing power were also significantly increased with the AP content and fermentation time. In the consumer acceptance test of APY, APY1.25 had significantly high scores in overall acceptance, taste acceptance, and aftertaste acceptance with purchase intent (p < 0.05). The Greek yogurt fortified with APS as functional food had improved antioxidant properties and consumer acceptance, suggesting the possibility of developing sustainable AP products.

Integrated Transcriptomic and Metabolomic Analysis of the Mechanism of Foliar Application of Hormone-Type Growth Regulator in the Improvement of Grape (Vitis vinifera L.) Coloration in Saline-Alkaline Soil

(1) Background: To solve the problems of incomplete coloration and quality decline caused by unreasonable use of regulators in grapes, this study clarified the differences in the effects of a hormone-type growth regulator (AUT) and two commercial regulators on grape coloration and quality through field experiments. (2) Methods: The color indexes (brightness (L*), red/green color difference (a*), yellow/blue color difference (b*), and color index for red grapes (CIRG)) of grape fruit were measured using a CR-400 handheld color difference meter. The titratable acid content, total phenol content, and total sugar content were measured using anthrone colorimetry, folinol colorimetry, and NaOH titration, respectively, and the chalcone isomerase activity, phenylalanine ammoniase activity, dihydroflavol reductase activity, and anthocyanin content were measured using a UV spectrophotometer. (3) Results: The a*, total sugar and total phenol contents, and chalcone isomerase (CHI) and phenylalanine ammoniase (PAL) activities of grape fruit in the AUT treatment significantly increased, while the titratable acid content significantly decreased, compared to those in the CK treatment. The expressions of the differentially expressed genes (DEGs) trpB and argJ in AUT treatment were significantly up-regulated. The expressions of the differentially expressed metabolites (DEMs) phenylalanine and 4-oxoproline were significantly up-regulated, while those of 3,4-dihydroxybenzaldehyde and N-acetyl glutamate were significantly down-regulated. The CIRG significantly increased by 36.4% compared to that in the CK, indicating improved fruit coloration. (4) Conclusion: The AUT could shorten the color conversion period of grape fruit and improve the coloration, taste, and tolerance to saline and alkaline stresses.