Removal of C9-aldehydes and -alcohols from melon juice via cysteine addition

BACKGROUND

The aroma of a melon fruit is among the most crucial qualities that influence consumer preferences. However, strong grassy and cucumber-like aromas can prevent consumer acceptance. These grassy and cucumber-like aromas are produced by aldehydes containing nine-carbon chains. Several studies have revealed that aldehydes exhibit a high affinity toward cysteine. Thus, the effect of adding cysteine to volatile compounds to melon juice was investigated.

RESULTS

The volatile compounds released from the melon juice were analyzed via solid-phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC-MS) after 0.5, 5, and 24 h of adding cysteine. The results indicated that the concentrations of aldehydes, such as (E,Z)-2,6-nonadienal and (E)-2-nonenal, in the melon juice decreased after the addition of cysteine at all the analyzed times. Additionally, (E)-2-nonenol and (E,Z)-2,6-nonadien-1-ol, which were formed by the enzymatic reduction of the aldehydes, also decreased by cysteine addition. To confirm the binding of cysteine with the aldehydes, two cysteine adducts were analyzed via liquid chromatography-mass spectrometry (LC-MS) employing (E)-2-nonenal in the melon juice after the addition of cysteine.

CONCLUSION

This study demonstrates that cysteine addition could be potentially used to reduce the grassy and cucumber-like aromas of melon juice. © 2022 Society of Chemical Industry.

High-Intensity Ultrasound Processing Enhances the Bioactive Compounds, Antioxidant Capacity and Microbiological Quality of Melon (Cucumis melo) Juice

The bioactive compounds, antioxidant capacity and microbiological quality of melon juice processed by high-intensity ultrasound (HIUS) were studied. Melon juice was processed at two ultrasound intensities (27 and 52 W/cm2) for two different processing times (10 and 30 min) using two duty cycles (30 and 75%). Unprocessed juice was taken as a control. Total carotenoids and total phenolic compounds (TPC) were the bioactive compounds analyzed while the antioxidant capacity was determined by DPPH, ABTS and FRAP assays. The microbiological quality was tested by counting the aerobic and coliforms count as well as molds and yeasts. Total carotenoids increased by up to 42% while TPC decreased by 33% as a consequence of HIUS processing regarding control juice (carotenoids: 23 μg/g, TPC: 1.1 mg GAE/g), gallic acid and syringic acid being the only phenolic compounds identified. The antioxidant capacity of melon juice was enhanced by HIUS, achieving values of 45% and 20% of DPPH and ABTS inhibition, respectively, while >120 mg TE/100 g was determined by FRAP assay. Further, the microbial load of melon juice was significantly reduced by HIUS processing, coliforms and molds being the most sensitive. Thus, the HIUS could be an excellent alternative supportive the deep-processing of melon products.

Antimicrobial efficacy of Lippia citriodora natural extract against Escherichia coli and Enterococcus faecalis in "Piel de Sapo" melon juice

BACKGROUND

The minimal inhibitory concentration (MIC) of an aqueous extract of Lippia citriodora with reported functional properties (PLX®) was determined on two strains of Escherichia coli (E. coli) belonging to serogroups commonly associated with foodborne illnesses (E. coli O157:H7 ATCC 700728 and E. coli O111 isolate 172) in vegetable products and two control strains for antimicrobial tests assays (E. coli ATCC 25922 and Enterococcus-En. faecalis ATCC 29212).

RESULTS

Mean MIC values at standard pH (7.4) in broth for the E. coli strains tested ranged from 4,444 µg/ml (35ºC) to 1,250 µg/ml (10ºC) and to 182 µg/ml (4ºC). At pH 5.5, conditions resembling those of melon juice, MIC was about 2 times higher at 35 and 10ºC compared with 4ºC. The MIC of En. faecalis was similar or slightly lower than those of E. coli at the conditions tested. In melon juice fortified with PLX® (2,500 µg/ml, maximum sensorial acceptable limit), the three strains of E. coli maintained their viability although none showed growth potential after 4 days at 4ºC.

CONCLUSIONS

PLX® could be added to melon juice to control E. coli O157:H7 and E. coli O111 during refrigerated storage, reducing the risk of microbiological contamination in this food.

Study of the Inhibitors of Cooked Off-Flavor Components in Heat-Treated XiZhou Melon Juice

This research applied inhibitors to reduce the content of cooked off-flavor components (dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, and 3-(methylthio)propanaldehyde) in heat-treated melon juice. The effects of glucose oxidase (GOD) on the formation and release of these four volatile sulfur compounds were also investigated. Results showed that GOD strongly inhibited the formation of the four compounds. In GOD-treated melon juice, S-methylmethionine was strongly protonated and not easily degraded into dimethyl sulfide. Moreover, the release of the dimethyl sulfide that did form was restrained by the hydrophobic interactions of gluconic acid and oxidation by hydrogen peroxide. In addition, gluconic acid (or glucose) and hydrogen peroxide could form a stable complex with methionine in an acidic matrix and thus prevented the methionine from producing 3-(methylthio)propanaldehyde, dimethyl disulfide, and dimethyl trisulfide by the Maillard reaction during heat processing.