EVALUATION OF INSTRUMENTAL METHODS FOR FIRMNESS MEASUREMENT OF FRESH AND CANNED CLINGSTONE PEACHES

The firmness of fresh and canned clingstone peaches was investigated using blade extrusion, back extrusion, and shear-compression instruments. The three techniques yielded results which correlated well among themselves and to sensory evaluation of peach firmness. Results indicate that high vacuum flame sterilization yields a canned product which is closer in firmness to fresh peaches than is the conventionally retorted product.     

MATURITY STANDARDS FOR PROCESSING CLINGSTONE PEACHES

The flesh color of 5 clingstone peach cultivars was measured (in CIELAB coordinates) by tristimulus colorimeter before and after canning. Before canning, fruit were separated into 3 color classes (1A: green-yellow, 4A: yellow-green, 7A: orange) by visual comparison with a trial maturity chart. After canning, flesh color was measured and visually graded. All samples in color class 1A were rated USDA grade C, while classes 4A and 7A were rated grade A. Flesh color was also measured as a function of time before and after harvest. Fresh flesh L* values were approximately constant, a* values increased steadily, and b* values increased then slightly decreased. Final specifications for a new maturity chart were 7 colors of constant luminance (L*= 76.5) and linearly increasing a* and b* values (?5.0 to 13.0 and 70.1 to 76.4, respectively), corresponding to a time step of 3.5 days between colors.     

POSTHARVEST CHANGES OF PECTIC SUBSTANCES IN CHILLED PEACHES

ABSTRACT Red Globe peaches were harvested at the threshold-mature stage and either stored at OC after preripening at 20C for 48 h or stored directly at 2C. Total pectin increased from 7.49 mg/g fresh weight in the threshold-mature sample to 10.21 mg/g in pre-ripened fruit stored at OC and 12.83 mg/g in fruits stored directly at 2C. Depending on extraction and storage protocol, between 26% and 73% of total pectin was solubilized. Chelator-soluble fractions had a low degree of esterification (DE ca. 20%), whereas other fractions were highly methylated (DE ca. 56% to 74%). Average DE did not vary between samples. DEAE-cellulose chromatography revealed an uneven distribution of methoxyl groups. Two prominent peaks were observed in chromatograms of chelator-soluble extracts from threshold-mature fruit and fruit stored directly at 2C. One peak was observed in chelator-soluble pectin from preripened fruit stored at OC.     

CHANGES IN TEXTURAL CHARACTERISTICS OF PANEER IN READY-TO-EAT CANNED PANEER CURRY DURING STORAGE

Paneer is an Indian soft cheese obtained by coagulating hot milk using citric acid or vinegar, pressing the hot coagulum and cooling by dipping in chilled water. In this study, paneer curry with a water activity (A_w) of 0.95 and a pH of 5.0 was prepared using ingredients like tomatoes, onions, cream, milk powder, curds and different spices, then canned at an F value of 0.80 (lethality). The product was stored at 15, 30 and 45C, and change in textural characteristics during storage was studied. Cohesiveness and chewiness increased, but hardness decreased. These changes were attributed to continued changes in texture initiated by frying of paneer and canning process. These were also linked to Maillard browning which progressed during storage as measured by hydroxymethylfurfural content. These changes were found to be slower vis‐à‐vis those observed in the product, which was sterilized at conventional F value of 15.0 (control) (A_w = 0.98 and pH 5.2).     

IDENTIFICATION OF THE MAIN TEXTURAL CHARACTERISTICS OF CANNED PEACHES AND THE EFFECTS OF PROCESSING VARIABLES

The texture profile of canned peach fruits was studied using magnitude estimation as a scaling method. Their sensory characteristics were assessed using as a modulus either a model fruit or a real fruit sample. The sequence of appearance of the textural characteristics was determined during 4 stages of assessment (nonoral, first bite, during mastication, after effects). Four different varieties of peach fruits were canned and the effect of four processing variables (level of heat treatment, degree of ripeness, sugar concentration in the processing liquid and hardness of the processing liquid) on the texture profile of the fruits was examined. The results showed that an increase in the severity of the heat treatment and the degree of ripeness of the fruit resulted in a decrease in the firmness, crunchiness and chewiness of the canned fruit. Fibrousness was similarly affected but to a lesser extent. Freshness and juiciness were also negatively affected by these variables. An increase in the sugar concentration and hardness of the processing liquid resulted in an increase in the firmness, crunchiness and chewiness of the canned fruit. Fibrousness, freshness and juiciness were similarly affected but to a lesser extent.     

CHANGES IN THE FREE SUGAR CONTENT OF BARLEY KERNELS DURING MATURATION

The free sugars extracted from kernels of a two-row barley variety, Betzes, were separated and determined quantitatively as negatively-charged borate derivatives by anion-exchange chromatography on substituted polystyrene resin. Sugars were determined at 2 or 3 day intervals immediately following anthesis, until kernels achieved harvest ripeness. Initially, the free sugars accounted for 6.5% of kernel dry matter; reducing sugars comprised 80% of the total free sugars, primarily as fructose (3% of the kernel dry matter) and glucose (2% of kernel dry weight), with lesser amounts of galactose, mannose, and maltose. Sucrose was the principal non-reducing sugar (1.8% of the kernel dry weight), but traces of raffinose were also detected. As kernel dry matter increased, the relative amount of free sugars decreased rapidly and comprised 2% of the kernel dry matter in mature kernels. At harvest ripeness, non-reducing sugars comprised 90% of the total free sugars. Sucrose decreased slightly from 1.8 to 1.2% of total kernel dry matter, but actually increased from 90 μg in immature kernels to 500 μg in mature kernels; raffinose increased relative to kernel dry matter from trace amounts 20 days after anthesis to 0.7% of kernel dry matter (i.e., 250 μg/kernel) 36 days after anthesis, and declined to 0.4% in mature kernels. Non-reducing, soluble fructosans were present at all stages of kernel maturation, but were not determined quantitatively.     

DEAN QUALITY: CHANGES IN HPLC PROFILES OF ACETIC ACID-EXTRACTABLE PROTEINS DURING STORAGE1

Samples of black beans (Phaseolus vulgaris L. cv. Orfeo) either dried in the field or by using heat treatment were stored for 3, 6 and 9 months under normal (15°C, 35% RH) and extreme conditions (30°C, 85% RH) to produce cotyledon hardness. After storage the cotyledon proteins were extracted with 5M acetic acid solution and the clarified extracts were analyzed by reversed-phase HPLC. The two drying procedures did not affect the HPLC chromatographic data. Samples that showed a gradual increase in cotyledon hardness showed quantitative and qualitative changes in HPLC chromatograms. Overall extractability of proteins was reduced in samples stored for nine months under high temperature and high humidity.