Postharvest Management of Fruits and Vegetables-Series II.

Fruits and vegetables are crucial nutritional sources of carbohydrates, protein, minerals, vitamins, and dietary fiber, offering significant benefits to human health [...].

Functional Characteristics of Aldehyde Dehydrogenase and Its Involvement in Aromatic Volatile Biosynthesis in Postharvest Banana Ripening.

Butanol vapor feeding to ripe banana pulp slices produced abundant butyl butanoate, indicating that a portion of butanol molecules was converted to butanoate/butanoyl-CoA via butanal, and further biosynthesized to ester. A similar phenomenon was observed when feeding propanol and pentanol, but was less pronounced when feeding hexanol, 2-methylpropanol and 3-methylbutanol. Enzymes which catalyze the cascade reactions, such as alcohol dehydrogenase (ADH), acetyl-CoA synthetase, and alcohol acetyl transferase, have been well documented. Aldehyde dehydrogenase (ALDH), which is presumed to play a key role in the pathway to convert aldehydes to carboxylic acids, has not been reported yet. The conversion is an oxygen-independent metabolic pathway and is enzyme-catalyzed with nicotinamide adenine dinucleotide (NAD+) as the cofactor. Crude ALDH was extracted from ripe banana pulps, and the interference from ADH was removed by two procedures: (1) washing off elutable proteins which contain 95% of ADH, but only about 40% of ALDH activity, with the remaining ALDH extracted from the pellet residues at the crude ALDH extraction stage; (2) adding an ADH inhibitor in the reaction mixture. The optimum pH of the ALDH was 8.8, and optimum phosphate buffer concentration was higher than 100 mM. High affinity of the enzyme was a straight chain of lower aldehydes except ethanal, while poor affinity was branched chain aldehydes.

Antioxidative Responses to Pre-Storage Hot Water Treatment of Red Sweet Pepper (Capsicum annuum L.) Fruit during Cold Storage.

The effects of hot water treatments on antioxidant responses in red sweet pepper (Capsicum annuum L.) fruit during cold storage were investigated. Red sweet pepper fruits were treated with hot water at 55 °C for 1 (HWT-1 min), 3 (HWT-3 min), and 5 min (HWT-5 min) and stored at 10 °C for 4 weeks. The results indicated that HWT-1 min fruit showed less development of chilling injury (CI), electrolyte leakage, and weight loss. Excessive hot water treatment (3 and 5 min) caused cellular damage. Moreover, HWT-1 min slowed the production of hydrogen peroxide and malondialdehyde and promoted the ascorbate and glutathione contents for the duration of cold storage as compared to HWT-3 min, HWT-5 min, and control. HWT-1 min enhanced the ascorbate-glutathione cycle associated with ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, but it was less effective in simulating catalase activity. Thus, HWT-1 min could induce CI tolerance in red sweet pepper fruit by activating the ascorbate-glutathione cycle via the increased activity of related enzymes and the enhanced antioxidant level.

Inhibition of acetate ester biosynthesis in banana (Musa sapientum L.) fruit pulp under anaerobic conditions.

The effect of anaerobic conditions on acetate ester biosynthesis in ripened banana pulp was investigated. Incubation of the pulp in less than 1% O(2) resulted in a significant reduction in the formation of ethyl acetate. Regardless of the presence of a large amount of endogenous ethanol and the remaining exogenous isobutyl alcohol after complete anaerobic incubation with the pulp, the production of acetate ester decreased. The effect of addition of pyruvate, isobutyl alcohol, acetate, and methyl hexanoate on acetate ester formation in 100% N(2) was also investigated. The addition of pyruvate and isobutyl alcohol to the pulp gave lower acetate esters in N(2) than in air, whereas the pulp incubated with acetate and isobutyl alcohol produced more acetate ester in both conditions. Therefore, the lack of acetyl CoA, or more precisely acetate, in the tissue is the main reason for the inhibition of acetate ester formation under anaerobic conditions. The activity of beta-oxidation measured by incubation with methyl hexanoate was detected only in the samples incubated in air. The formation of acetyl CoA, derived from pyruvate through mitochondria and through beta-oxidation, was inhibited by anaerobic conditions, which suggests that mitochondrial activity and/or beta-oxidation are essential for ester biosynthesis.

Reversible and irreversible emission of methanethiol and dimethyl disulfide from anaerobically stored broccoli.

The reversible and irreversible emission of methanethiol (MT) and dimethyl disulfide (DMDS) from broccoli florets was demonstrated during anaerobic storage at 20 degrees C for up to 24 h. Reversible emission of MT and DMDS was feasible only in broccoli stored for between 0 and 12 h under entirely anaerobic condition. Beyond that, the emission was completely irreversible. This irreversible process was demonstrated through significant reductions in the chlorophyll fluorescence values and rate of carbon dioxide production and significant increase in the membrane permeability of induced broccoli tissues after exposure to air and incubation. Irreversible emission was also demonstrated through significant change in color from the characteristic bright green to olive green as well as the conversion of chlorophyll a to pheophytin a and chlorophyll a' contents of the induced florets after hot-water treatment. These findings suggest that the irreversible emission of MT and DMDS is a function of permanent membrane damage and loss of intracellular compartmentation in the broccoli tissues as a result of the anaerobic induction. The off-odor formation can still be reversed if the affected tissue is only temporarily impaired by anaerobic condition, thereby maintaining the quality of stored broccoli.

Formation of methanethiol and dimethyl disulfide in crushed tissues of broccoli florets and their inhibition by freeze-thawing.

The formation of methanethiol and dimethyl disulfide in crushed, homogenized, and frozen-thawed tissues of broccoli florets was investigated. These volatile sulfur compounds were produced in crushed florets, but their formation was inhibited in frozen-thawed tissues. Only dimethyl disulfide was formed in homogenized tissues. High pH treatment triggered the release of dimethyl disulfide in frozen-thawed tissues and also enhanced the action of cysteine sulfoxide lyase in all disrupted tissues. Methyl methanethiosulfinate and methyl methanethiosulfonate were not detected in crushed florets; thus, the favored mechanism for the formation of methanethiol and dimethyl disulfide is the chemical disproportionation of methanesulfenic acid. In contrast, the formation of dimethyl disulfide in frozen-thawed and homogenized tissues occurs from the chemical disproportionation of methyl methanethiosulfinate that was detected in these tissues. The inhibition of dimethyl disulfide production during freeze-thawing must be caused by a sudden drop in the pH of the tissue, adherence of dimethyl disulfide on the tissue surfaces, and weakening of the cysteine sulfoxide lyase activity under acidic conditions.