Water-Holding Capacity in Hard-to-Cook Beans (Phaseolus vulgaris): Effect of pH and Ionic Strength

The effect of pH and ionic strength (IS) of soaking solution on the water holding capacity (WHC) of hard-to-cook (HTC) and control black beans (Phaseolus vulgaris) was evaluated. Beans were soaked 18 hr in solutions covering the pH range 1–7 at constant IS (1.0 M) or in solutions ranging in IS from 0.01 to 1.3M (prepared with either NaCl or CaCl₂) at pH 7. WHC was significantly reduced in the pH range 3.5 to 5.1 in control beans but the effect was not as pronounced with HTC samples which had a lower WHC at each pH. Solutions prepared with NaCl produced significantly lower WHC values than CaCl₂ solutions in the control but not in the HTC beans. WHC values in control beans tended to increase with higher IS, although this effect was not as apparent for HTC beans.     

TOUGHENING IN BLANCHED ASPARAGUS: IDENTIFICATION OF PHENOLIC COMPOUNDS AND EVIDENCE FOR A FREE RADICAL MECHANISM

Prior research in this laboratory established apparent nonenzymatic toughening occurs in heat treated asparagus tissue. The present work attempted to identify the phenol compounds involved and to discern the mechanism(s) of this reaction. Toughness (Warner-Bratzler shear) of blanched (no detectable per-oxidase or polyphenol oxidase activity) spears stored at 22°C increased significantly over a 4 day period. Reverse phase-high pressure liquid chromatography (RP-HPLC) of methanolic tissue extracts indicated 7 major phenolic peaks. HPLC retention times and Fourier transform-infrared spectroscopy tentatively identified the extracted phenols as: (1) 4-hydroxybenzoic acid; (2) caffeic acid; (3) vanillic acid; (4) syringic acid; (5) p-coumaric acid; (6) syringaldehyde; and (7) ferulic acid. A significant decrease in the concentration (HPLC peak area) of 1, 2, 5, 6 and 7 occurred after 4 days storage. In vitro studies with homogenized (blanched and unblanched) asparagus tissue indicated a significant decrease in the concentration of added phenols. Unblanched tissue produced greater changes. The site of added phenol incorporation (a significant increase in fluorescence intensity) was determined to be the vascular bundle region. Metal ion chelation (EDTA), addition of iron (Fe²⁺) and reduction of metal ions using L-ascorbic acid affected added phenol utilization variably. Only the addition of a mixed antioxidant (BHA, PG, citric acid) served to significantly decrease utilization of the added phenols by blanched tissue blends, therefore implicating a free radical mediated phenol coupling mechanism. ESR spectroscopy detected the ascorbate radical anion in the blanched homogenate.     

Low Temperature Blanching Effects on Chemistry, Firmness and Structure of Canned Green Beans and Carrots

Green beans and carrots were canned using extended blanching at 64–65°C and added calcium and/or acid. Firmer products resulted from all treatments but lowered pH was most effective. Blanched green beans were firmer with lower pectin esterification, indicating pectin methyl esterase activity. Green beans and carrots treated with calcium and/or acid and then cooked were firmer than controls. Acid exhibited a firming effect, perhaps by loosening tissue, while calcium reduced the influence of heat. Instrumental bioyield values correlated with sensory results of canned green beans; bioyield may result from a scleriformic layer. Microscopy showed firmer beans had intact middle lamellae while softer samples contained separated cells. These data suggest that the treatments rendered pectates in the middle lamella less heat labile.     

Respiratory Enzyme Activity in Low Temperature Sweetening of Susceptible and Resistant Potatoes

During storage at 4°C and 12°C, a potato cultivar susceptible to chill-sweetening (Norchip) accumulated significantly (P≤0.05) higher levels of sucrose, fructose and glucose than a potato selection resistant to chill-sweetening (ND 860-2). ND 860-2 tubers exhibited a significantly (P≤0.05) higher respiration rate throughout storage, reflected in higher activities of phosphofructokinase (PFK), glucose-6-phos-phate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). Storage significantly (P≤0.05) reduced respiration rate for both cultivars. G6PDH showed no significant (P>0.05) difference in specific activity or V_max between 4°C and 12°C for either cultivar. However, Km decreased at 4°C for both cultivars, possibly due to build up of substrate.     

Effect of Low Temperature Storage on Sugar Concentrations and Chip Color of Certain Processing Potato Cultivars and Selections

Two potato cultivars (Kennebec and Simcoe) and one selection (ND 860–2) were stored for 3 months at 4°, 9° and 11°C. ND 860–2 had the lowest sugar content at all storage temperatures, produced the lightest colored chips and was the only sample which gave acceptable colored chips directly from 4°C storage. In another study, three potato cultivars (Norchip, Simcoe and Onaway) and one selection (ND 860–2) were evaluated for sugar content and chip color during growth and harvest, two weeks prior and two weeks after foliar senescence, and stored under various time —- temperature regimes and upon reconditioning. ND 860–2 generally had the lowest levels of fructose, glucose and sucrose and Onaway had the highest. Storage at 5°C resulted in increases in the three sugars for all tubers, sucrose showing the most notable increase. ND 860–2 was the only sample to consistently produce acceptable colored chips directly from 5°C.     

Changes in the Melting Characteristics of Bovine Tendon Collagen Induced by a Bacterial Collagenase

Differential scanning calorimetry was used to study the changes produced by a commercial Clostridium histolyticum collagenase preparation on the melting behavior of bovine Achilles tendon collagen. The samples were heated at 5°C/min from 25 to 100°C. As a result of proteolysis, the collagenase-treated samples were partially gelatinized at 25°C and, during the calorimetric experiments, exhibited significant decreases in their melting transition parameters when compared to intact collagen. The denaturation temperatures and enthalpies obtained were 61.6°C and 44.4 J/g sample for intact collagen and 43.6°C and 26.1 J/g sample for collagenase-treated collagen. These differences may be accounted for by changes produced in the structural organization of the collagen fibrils by the collagenase treatment.