INFLUENCE OF THE SKIN ON PUNCTURE PROPERTIES OF CHILLED AND NONCHILLED TOMATO FRUIT

The puncture properties (firmness, toughness) of tomato skin and its influence on the overall puncture properties of mature-green fruit during ambient temperature (22C) ripening or chilled (5C) storage were estimated from the difference between whole fruit puncture force-deformation behaviour and that measured with the skin removed. Although the firmness of the skin of nonchilled fruit did not change significantly (p > 0.05) over 28 days of ripening, its contribution to overall puncture firmness increased from about 25 to 70%. Both skin toughness and its contribution to overall puncture toughness doubled within the first week of ripening of nonchilled fruit. The firmness of chilled fruit skin decreased (p > 0.05) only after 16 days of storage, but its contribution to overall puncture firmness remained constant at 25–30%. Both the toughness of the skin of chilled fruit and its contribution to overall puncture toughness remained constant during storage. Possible artifacts in the measurement of puncture properties of chilled fruit are discussed. The results are consistent with a toughening of tomato skin during early stages of ripening of nonchilled fruit that somewhat compensates for a rapid reduction in pericarp tissue integrity, and with an increase in firmness or rigidity of tomato skin and underlying tissue(s) during chilled storage of fruit.     

HPLC Determination of Caffeine and Theobromine in Coffee, Tea, and Instant Hot Cocoa Mixes

Popular brands of instant and ground coffee, instant and bag tea, and instant hot cocoa mixes were prepared according to manufacturer's directions and analyzed for caffeine and/or theobromine content. After extraction into boiling water, the methylxanthines were separated by high performance liquid chromatography using a reverse phase C₁₈ column and a mobile phase of acetonitrile and water (8:92, v/v). Caffeine content ranged from 32.4–35.0 mg/cup in instant tea, 30.2–67.4 mg/cup in bag tea, 1.0–7.8 mg/cup in instant hot cocoa mixes, 46.7–67.6 mg/cup in instant coffee, and 93.0–163.5 mg/cup in ground coffee. Theobromine concentrations ranged from 1.4–2.3 mg/cup in instant tea, 1.2–4.4 mg/cup in bag tea, and 39.5–79.5 mg/cup in instant hot cocoa mixes.     

Chilling-Associated Softening of Tomato Fruit is Related to Increased Pectinmethylesterase Activity

Mature-green tomatoes chilled 15 days (5°C; RH >85%) were softer than nonchilled during subsequent ripening (22°C) by both whole fruit and pericarp tissue puncture (p<0.05), but not by flat-plate compression. No differences in total polygalactnronase (PG) or PG isozyme activity were evident although total activity was greater in nonchilled after 10 days ripening. Softening of nonchilled fruit correlated (p<0.05) with extracted PGI activity, while chilling-associated softening correlated (p<0.05) with higher initial extracted pectinmethylesterase (PME) activity. Extracted peroxidase remained constant throughout ripening but was greater (p<0.05) in pre-chilled fruit consistent with chill-induced membrane dysfunction. Transmission electron microscopy showed the middle lamella from pre-chilled tomatoes was swollen and less defined. Loss of turgor from translocation of water to the PME-modified cell wall was suggested to be responsible for softening as a consequence of chilling.     

PROTEIN-PHYTATE INTERACTION IN SOYBEANS. III. THE EFFECT OF PROTEIN-PHYTATE COMPLEXES ON ZINC BIOAVAILABILITY

A study was conducted to determine the influence of pH on the chemical form of phytate in a commercial soy isolate and its effect on zinc bioavailability by monitoring weight gain in weanling rats. Ultrafiltration studies demonstrated that the free phytate content of soy isolate solutions was greatest at pH 5.0; above this the neutralization of soy isolates resulted in the formation of a soluble proteinphytate complex. The bioavailability of zinc from diets providing protein from egg, acid and neutral soy isolates and containing various levels of added zinc was measured. The growth of rats receiving zinc from the neutral soy isolate was significantly lower than that of rats deriving zinc from either the acidic soy isolate or egg white diets. It is proposed that the reduction in bioavailability of zinc caused by the neutralization of soy protein isolate is related to the formation of a protein-zinc-phytic acid complex resistant to hydrolysis in vivo.     

Specific Permeability of Porous Compacts as Described by a Capillary Model

The specific liquid permeabilities of a wide variety of phosphatebonded, porous alumina compacts prepared from alumina powders of differing size distribution, and ranging in porosity from 32 to 50 vol%, were not described well by the Carmen-Kozeny model but were described by a capillary model based on mean entry pore radius. The specific permeability varied directly with the square of the mean entry pore radius determined by mercury intrusion. The compacts containing the lowest phosphate bond phase obeyed Poiseuille's law.     

Growth of Beryllia Single Crystals

Single crystals of beryllia have been grown by two methods. One method exploits the high-temperature reversible reaction BeO + H₂O.Be(OH)₂. The other is a flux method, in which BeO is dissolved and precipitated as single crystals in a lithium molybdate flux. Characteristics and remaining problems of the two methods are discussed, and the crystals produced are described.     

Fluorescence Intensity Indicates Bean Hardening

Fluorescence microscopy was used to measure the intensity of fluorescent emanation from the cut surface of uncooked bean cotyledons. This parameter correlated significantly with the hardness of soaked cooked beans determined by either compression force of whole beans or the probe force of cotyledons only. This relationship existed whether hardness resulted from varietal differences or elevated storage conditions. Similarly, a significant correlation was found between the fluorescence intensity of isolated cell wall material and bean hardness. These results led to the conclusion that the increase in fluorescence intensity in hard beans may have been due to the accumulation of phenolic compounds within the cell wall and that the procedure developed had potential as a quicker and simpler way to determine bean hardness.     

CHILLING INJURY. A REVIEW OF QUALITY ASPECTS

The various quality aspects of chilling injury (CI) serve as the focus of this review in which symptoms, occurrence and its alleviation are discussed. CI is a term used to describe the physiological damage that occurs in many plants and plant products, particularly those of tropical and subtropical origin, as a result of their exposure to low but nonfreezing temperatures. The substantial economic consequences of CI have provided the impetus for studying/developing effective means of alleviating symptoms which manifest this disorder. A diversity in plant responses to low temperature stress exists, including alterations in ethylene biosynthesis, increased respiration rates, cessation of protoplasmic streaming, increased solute leakage, and uncoupling of oxidative phosphorylation. These various responses ultimately give rise to an array of visual symptoms (e.g., surface pitting, water rot, poor color development, general loss of structural integrity) which can render severe losses in product quality both pre- and postharvest. A number of different methods are available by which to alleviate symptom development, including manipulation of storage conditions (e.g., temperature cycling, hypobaric and modified atmosphere storage), exogenous chemical treatments (e.g., application of phospholipids, antioxidants, calcium) and genetic modification of chill sensitive species. These are discussed with respect to their effectiveness and possible control mechanisms.