Differential sensitivity to thermal processing of two muskmelon cultivars with contrasting differences in aroma profile

Synergistic effect of microwave heating and thermosonication on the physicochemical and nutritional quality of muskmelon and sugarcane juice blend

Melons (Cucumis melo L.) are highly popular due to its delicate and delightful flavor in the worldwide. However, the flavor of the melon juice was easily affected by thermal treatments and unpleasant cooking smell during production process. Sugarcane (Saccharum officinarum) juice is a proven nutritious beverage with high levels of antioxidants, polyphenols, and other beneficial nutrients. Due to its low sugar content, combined with sugarcane, muskmelon-sugarcane blend juice gives an appealing and exotic drink. The research was planned to evaluate the effect of thermo-sonication (20 kHz, 70% amplitude, 5, 10 and 15 min) and microwave (90 °C, 400 W, 120 sec) on physicochemical parameters including pH, titratable acidity, total soluble solids (TSS), total phenolic contents (TPC), total flavonoid contents (TFC) and antioxidant capacity of muskmelon and sugarcane juice blend, during storage of 90 days at refrigeration (4±1 °C). The statistical results showed that synergism of sonication and microwave treatments had a significant (p ≤ 0.05) influence on pH, TSS, titratable acidity, TPC, TFC and antioxidant capacity. T₃ (15 min of sonication and 120 s of microwave) showed the maximum TSS (12.00±0.40 °B), pH (5.07±0.02), TPC (484.33±10.41 mg GAE/100 mL), TFC (261.73±11.32 mg CE/100 mL), and antioxidant activity (381.62±17.72 µg AAE/100 mL), as compared to untreated samples. Thermosonication for 15 min caused maximum retention of TPC, TFC and antioxidant capacity of blend juice during 90 days of storage, whereas in untreated samples these parameters were found highly decreased during storage. Thus, sonication and microwave can be recommended as an alternative to both conventional pasteurization processes and chemical preservatives.

Postharvest chilling diminishes melon flavor via effects on volatile acetate ester biosynthesis

In postharvest handling systems, refrigeration can extend fruit shelf life and delay decay via slowing ripening progress; however, it selectively alters the biosynthesis of flavor-associated volatile organic compounds (VOCs), which results in reduced flavor quality. Volatile esters are major contributors to melon fruit flavor. The more esters, the more consumers enjoy the melon fruit. However, the effects of chilling on melon flavor and volatiles associated with consumer liking are yet to be fully understood. In the present study, consumer sensory evaluation showed that chilling changed the perception of melon fruit. Total ester content was lower after chilling, particularly volatile acetate esters (VAEs). Transcriptomic analysis revealed that transcript abundance of multiple flavor-associated genes in fatty acid and amino acid pathways was reduced after chilling. Additionally, expression levels of the transcription factors (TFs), such as NOR, MYB, and AP2/ERF, also were substantially downregulated, which likely altered the transcript levels of ester-associated pathway genes during cold storage. VAE content and expression of some key genes recover after transfer to room temperature. Therefore, chilling-induced changes of VAE profiles were consistent with expression patterns of some pathway genes that encode specific fatty acid- and amino acid-mobilizing enzymes as well as TFs involved in fruit ripening, metabolic regulation, and hormone signaling.

Ultrasonic treatment maintains the flavor of the melon juice

Thermal treatment usually leads to the flavor deterioration of melon juice. This study was initiated to evaluate the retention effect of ultrasonic (US) and ultra-high pressure (UHP) on volatile components of melon juice by gas chromatography-mass spectrometer (GC-MS) and gas chromatography-ion mobility spectrometry (GC-IMS). The electronic nose, electronic tongue, and GC-IMS analysis showed that US was much better way to contain the flavor of melon juice than UHP was does. The correlation coefficient between the US and the control was as high as 0.99. The concentration of characteristic aroma components in melon juice after ultrasonic treatment was 2.77 times and 3.02 times higher than that in the control and UHP, respectively. Moreover, the US treatment gave no significant difference in the total soluble solids, pH, and color of the juice. And it dramatically enhanced the flavor profile of melon juice.

High-pressure treatment enhanced aromatic compound concentrations of melon juice and its mechanism

Introduction

The flavor deterioration blocks the development of melon juice.

Methods

The effects of ultra-high temperature (UHT) and high pressure (HP) treatments on the aromatic compound concentrations of melon juice and their mechanisms were explored with fresh juice as the control.

Results

A total of 57 volatile compounds were identified by gas chromatography-tandem mass spectrometry analysis. β-ionone was shown to be the major aromatic component of melon juice for the first time. The HP at 200 MPa for 20 min increased the total volatile concentration of melon juice by 1.54 and 3.77 times the control and UHT, respectively. Moreover, the sum concentration of a major aromatic component in the HP treatment was 1.49 and 5.94 times higher than that of the control and UHT, respectively.

Discussion

The HP treatment raised the concentration of volatile and aromatic components of melon juice by reducing their surface tension.

Surmounting the off-flavor challenge in plant-based foods

Plant-based food products have been receiving an astronomical amount of attention recently, and their demand will most likely soar in the future. However, their unpleasant, intrinsic flavor and odor are the major obstacles limiting consumer's acceptance. These off-flavors are often described as "green," "grassy," "beany," "fatty" and "bitter." This review highlights the presence and formation of common off-flavor volatiles (aldehydes, alcohols, ketones, pyrazines, furans) and nonvolatiles (phenolics, saponins, peptides, alkaloids) from a variety of plant-based foods, including legumes (e.g. lentil, soy, pea), fruits (e.g. apple, grape, watermelon) and vegetables (e.g. carrot, potato, radish). These compounds are formed through various pathways, including lipid oxidation, ethanol fermentation and Maillard reaction (and Strecker degradation). The effect of off-flavor compounds as received by the human taste receptors, along with its possible link of bioactivity (e.g. anti-inflammatory effect), are briefly discussed on a molecular level. Generation of off-flavor compounds in plants is markedly affected by the species, cultivar, geographical location, climate conditions, farming and harvest practices. The effects of genome editing (i.e. CRISPR-Cas9), various processing technologies, such as antioxidant supplementation, enzyme treatment, extrusion, fermentation, pressure application, and different storage and packaging conditions, have been increasingly studied in recent years to mitigate the formation of off-flavors in plant foods. The information presented in this review could be useful for agricultural practitioners, fruits and vegetables industry, and meat and dairy analogue manufacturers to improve the flavor properties of plant-based foods.