L. H. Aung

Conditioning and heat treatments influence flavedo soluble sugars of lemon

SummaryThe changes in flavedo soluble sugars of lemon, Citrus limon (L.) Burm. cv. Eureka, to conditioning and heat treatment were determined. Raffinose significantly increased with 3–6 d conditioning at 15·C with 85% relative humidity but sucrose significantly decreased in flavedo of lemons after 6 d of conditioning. Glucose and fructose contents were not altered significantly. Heat treatment of lemons at 55·C for 5 min significantly increased sucrose content of flavedo, but the raffinose content was unaffected while glucose and fructose contents decreased slightly. The content of fructose in green lemon flavedo was significantly lower than in yellow lemon flavedo, but the content of glucose, sucrose and raffinose tended to be slightly higher. The probable involvement of soluble sugars of lemon flavedo in moderating stress and in protecting cellular membranes from temperature extremes and desiccation is discussed.

Postharvest storage temperature and film wrap effects on quality of chayote, Sechium edule Sw

SummaryChayote fruit quality deteriorates with storage. At 25°C postharvest storage, fruit lost 1.3% of its fresh weight per day compared with 0.5% day–1 at 15°C or 0.02% day–1 at 10°C. The rate of weight loss was 2–5 fold greater at 25°C than at 15°C or 10°C. During the five weeks of storage, unwrapped fruit lost over 40% of their fresh weight at 25°C, 18.9% at 15°C and 13.0% at 10°C. The shrivelled appearance due to weight loss detracts from the utility, appeal and salability of the fruits. Wrapping the fruit in a commercial grade polyvinyl chloride (PVC) film significantly reduced weight loss. The weight loss for the five-week storage period of PVC wrapped fruit was 8.3% at 25°C, 4.0% at 15°C and 1.3% at 10°C. The best storage of fruits was obtained with PVC film wrap at 10°C. Firmness of the skin (exocarp) and flesh (mesocarp) of the fruit remained relatively unaffected by storage at 10°C–25°C. An average skin firmness of an edible chayote fruit measured 22.1 ± 2.7 N and the flesh 14.3 ± 0.8 N. The fi...

Postharvest conditioning temperatures and fruit maturity on flavedo soluble sugars of coastal and desert lemons

SummaryThe content and changes in flavedo soluble sugars of Citrus limon (L.) Burm. F. of different maturity derived from coastal and desert climatic regions to two postharvest conditioning temperatures of 158C and 108C were determined. Conditioning caused significant changes of flavedo soluble sugars in lemons of the two geographic areas. Raffinose level increased with duration of conditioning in both desert and coastal lemons and was slightly higher at 108C than at 158C conditioning. The flavedo sucrose content of green coastal lemons was greater than silver or yellow lemons and increased significantly in silver and yellow lemons after conditioning for 3 d at 158Cor108C, but declined significantly in all maturity classes to a low level with conditioning of more than 3 d. In contrast, the flavedo sucrose content of green and yellow desert lemons was 2.8–fold and 1.7–fold greater, respectively, than comparable coastal lemon flavedo, with the green lemon flavedo showing a significant gradual decrease with ...

Timing and control of methanethiol emission from broccoli florets induced by atmospheric modification

Storage of broccoli (Brassica oleracea L., Italica Group) under conditions of low O2, concentration extends its shelf life. Excessively low O2, however, leads to the formation of an offensive odour which is primarily due to the emission of methanethiol. In this study, we investigated the initial induction and control of methanethiol production of broccoli florets exposed to various levels of O2, and CO2, over short-term periods of 10 h or less. Lowering the O2 concentration surrounding the broccoli florets by continuously flowing N, through the sample containers acted to initiate the production of methanethiol within 1 h after the O2 concentration had reached 0.5%. After initiation the rate of production showed a slow but steady increase during the 10 h of experimentation. In contrast, introduction of O2 into the sample containers while the broccoli florets were actively producing methanethiol led to a rapid 79% drop in the amount of methanethiol detected within 15 min, followed by a complete absence of m...

Release of d-limonene from non-injured and injured lemons treated with hot water and low temperature

SummaryVolatile emanation from whole lemon fruits was determined following hot-water or cold treatments to examine the relationship between liberation of essential oils from the oil glands and the deleterious effects of these treatments. Headspace analysis indicated that β-pinene, d-limonene and -γ-terpinene were the most abundant volatiles, comprising 8, 42 and 21%, respectively, of the total amount. Due to its abundance, d-limonene was selected as the essential oil component to be quantified following treatment. Hot-water treatments for 10 min at 48°C and below were non-injurious to both yellow and green fruit, with injury in the form of lesions on the rind beginning to occur at 50°C (yellow) and 52°C (green), and increasing in severity up to 58°C, the highest temperature tested. D-limonene emanation increased correspondingly with increasing injury. Green lemons were injured more severely than yellow and tended to release more d-limonene, especially at higher temperatures. Curing at 15 and 20°C for 6 d ...

Heat-induced alteration of methanethiol emission from anaerobic broccoli florets

SummaryThe influence of heat applied before and during the imposition of anaerobic conditions on methanethiol (MT) production of broccoli (Brassica oleracea L. Italica group) was studied. Ten minute heat treatments of temperatures ranging from 40 to 60°C imposed on broccoli florets prior to the initiation of 18 h of anaerobic conditions strikingly altered the course of MT production and respiration. Heat treatment at 40 and 45°C greatly diminished MT production compared with 25°C during the first 6 h. In contrast, MT production was stimulated at 55°C and completely eliminated at 60°C. The respiratory rate of broccoli treated at 50°C was increased, whereas at 45, 55 and 60°C the rates were decreased compared with that of 25°C. The rate of respiration at 40°C was similar to that at 25°C. The amount of hydrogen sulfide (HS) and dimethyl disulfide (DMDS), two other sulfur gases also emitted under anaerobic conditions, was increased by heat treatment. Heat treatment given concurrently with the formation of MT ...

Changes in moisture, dry matter and soluble sugars of dry-on-the-vine raisins with special reference to sorbitol

Summary The moisture, dry matter and soluble sugar composition of Vitis vinifera L. advanced selections of dry-on-the-vine raisins were determined over several seasons. Moisture loss from post-veraison berries occurred in a graduated stepwise manner, with a rapid decline from an initial 86±2% to 60±5% 108 d from first bloom, a slower loss and a final accelerated loss to 25±4% after 151 days from first flowering. The pattern of dry-matter accumulation was similar in large, medium, or small berries but dry matter was higher in large (0.65±0.04 g dry wt. per berry) than medium (0.52±0.03 g dry wt. per berry) or small (0.36±0.03 g dry wt. per berry raisin). Incipient browning was seen with raisin formation at the distal berry region with a higher sugar concentration than in the proximal (pedicel) region. Sucrose in the raisins exhibited two maxima, one (1.4±0.2 mg g–1 fresh wt.) 96 d from first bloom, and a second (2.4±0.4 mg g–1 fresh wt) 123 d after first bloom, with each maximum occurring before the rise in glucose, fructose, and sorbitol, and decreasing as these sugars increased. Sorbitol was not detected initially in mature berries, but increased in raisins. It was proposed that sorbitol or its biosynthetic enzyme might be useful for determining raisin harvest. Raffinose and sucrose contents of the peduncle were higher than raisins and may indicate a role of these sugars in the physiology of the peduncle.

The distribution of carbohydrates in the organs of Sechium edule Sw.

SummaryQuantitative and qualitative aspects of carbohydrates in the organs of three chayote, Sechium edule Sw., genotypes were determined by high-performance liquid chromatography, thin-layer chromatography and colorimetric procedures. The total amount of ethanol-soluble sugars and of starch in the apical vegetative shoots of the genotypes did not differ significantly. The amount of sugars, however, within a genotype differs. There was twice as much glucose as sucrose and sorbitol and four times the amount of fructose as sucrose and sorbitol. The combined quantity of glucose and fructose in the shoots was six times greater than sucrose or sorbitol. The starch content in the root was 51% and in the tubers 72% on a dry-weight basis. In the immature fruit, the average starch content was higher in the seed (85 |xg mg-1 dry wt.) than in the flesh (75 (ig mg-1 dry wt.). The major chayote sugars were glucose, fructose, sucrose and sorbitol, and to a lesser extent, raffi-nose and stachyose. In addition, two unkno...

Heat shock induced changes in exocarp soluble sugars of lemons from two climatic regions

Summary Investigations were conducted to ascertain whether the 558C heat shock induced changes in soluble sugars of the exocarp(flavedo) of lemons, Citrus limon (L.) Burm. F., derived from two distinct climatic growing regions. The exocarp sugars of coastal- and desert-grown lemons were quantitatively different, but both geographically different lemonsresponded with sucrose increases to 558C heat shock of >3 min duration. However, the responses were influenced by fruit maturity and seasonal factors. When comparing the response of coastal- and desert-grown lemons to heat shock treatment, the exocarp sucrose levels were noteworthy. Heat shock significantly increased sucrose level of early-season coastal lemon more than mid- to late-season lemons. In contrast, late-season desert lemon showed a striking response to the heat shock treatment, with a greater increase in sucrose than mid- and early-season lemons. These results suggest a physiological basis for the differential responses to heat treatment of lemons from different geographical regions. The concomitant decreases of glucose and fructose and the sucrose increase with heat shock implied that the sucrose increase may be derived by synthesis from glucose and fructose.

EFFECT OF POSTHARVEST DESICCATION AT HIGH TEMPERATURE ON SOLUBLE SUGAR CHANGES OF TWO SUPERSWEET SWEET CORN CULTIVARS

The alteration in the soluble sugar contents of two commercial cultivars of sweet corn, Zea mays L. Supersweet Jubilee and Sweetie, desiccated at 60°C was determined. The loss of kernel moisture un...