Ascorbic Acid/Citric Acid Combinations in the Processing of Frozen Apple Slices

Sulfite replacement was investigated in a commercial apple freezing operation: Jonathan and Spy apple slices were vacuum-impregnated in 0.5% or 1% ascorbic acid (LAA) or D-araboascorbic acid (DAA). 0.25% or 0.5% citric acid (CA), 2h NaCl, and 0.25% CaCl₂ Treatments with DAA gave color and sensory properties equal to LAA treatments. Slice color was not significantly different between 0.5% and 1.0% ascorbic acid isomers and 0.25% or 0.5% CA. Shear measurements of Jonathan slices were significantly influenced by DAA and citric acid concentrations. Texture of Spy slices was not affected by treatment or storage. This study indicates that DAA may be substituted for more expensive LAA for treating Spy and Jonathan slices prior to freezing.     

Plum Juice Quality Affected by Enzyme Treatment and Fining

Juice from six plum (Primus domestica L.) cultivars, Au Red, Abundance, Pobeda, Shiro, Peach Plum and Early Golden, was extracted using 0.2% Clarex® L pectinase. The juice was processed as high temperature-short time (HTST)-unfined juice, fined juice or HTST-fined juice, and analyzed for yield, clarity, pectin content, soluble solids, pH, titratable acidity, color, sugars, total anthocyanins and total phenolics. Pectinase treatment resulted in 41–214% increase in juice yields, with highest increase for Au Red. Enzyme-extracted juice averaged 54% lower pectin than controls, and fining further reduced pectin. Enzyme treatment also improved juice soluble solids and color. A consumer type sensory panel indicated juice from Abundance, Pobeda and Peach Plum had best flavor and acceptability.     

PERFORMANCE OF AN INSTRUMENT DESIGNED FOR,AND EVALUATION OF METHODS TO ASSESS,PEACH FRUIT IMPACT BRUISE SUSCEPTIBILITY1

A simple, inexpensive device was fabricated for imposing drop impact loads on fruit and tested using a 0.5 J load on peach [(Prunus persica (L.) Batsch] fruit harvested at two maturity stages. The device consists of an electromagnet to secure a metallic mass above the fruit, a height adjustment for positioning the mass, a foot pedal switch for interrupting current to the electromagnet, allowing the mass to strike the fruit, and a thick aluminum base to prevent fruit movement upon impact. Following impact, fruit were stored at 2C for one week (to simulate impact damage during harvest and packing, prior to short term cold storage). Impact bruise susceptibility was assessed after storage by bruise occurrence (without regard to bruise size), and by bruise severity (measured as bruise depth, bruise width and bruise discoloration). Maturity at harvest had no effect on bruise occurrence, but did significantly effect bruise severity. Bruise depth was more sensitive than bruise width or discoloration to differences between cultivars. Cultivar ranking for bruise susceptibility differed, depending on the parameter used to obtain the ranking.     

PHYSICOCHEMICAL AND SENSORY CHARACTERISTICS OF SELECTED MICHIGAN SWEET CHERRY (Prunus avium L.) CULTIVARS

Sweet cherry cultivars grown in Northern Michigan in 1992 were analyzed for sensory and physicochemical characteristics. ‘Emperor Francis’, a yellow/red blushed, light color cultivar had the highest Brix/acid ratio at the 4th harvest, and it scored higher in sensory tests for sweetness flavor and overall acceptability than the dark cultivars, ‘Sam’ and ‘Hedelfingen’. Harvest dates showed significant effect on titrable acidity, Brix, Brix/acid ratio, sugars, weight and diameter of fruits. Brix/acid ratio showed significant correlation with sweetness. Correlation coefficients between overall consumer acceptability and measured parameters for three sweet cherry cultivars indicate that firmness has potential as an objective overall index for acceptability.     

Characterization of Polyphenoloxidase from Stanley Plums

Five plum cultivars were investigated for polyphenoloxidase. Stanley cultivar, which showed highest PPO activity, was selected for characterization of this enzyme. The activity of crude enzyme was 3.5 times greater in the flesh than in the skin of the fruit. The enzyme showed a K_m of 20 raM of catechol and V_max of 5.41 × 10^?1 O.D./ min at pH 6.0. Its pH and temperature optima were 6.0 and 20°C respectively. The enzyme lost activity below pH 4.5, but was stable even at 70°C. Among substrates, 4-methylcatechol was oxidized more rapidy, although catechol, dopamine, pyrogallol and caffeic acid were also good substrates. The enzyme was strongly inhibited by sodium metabisulfite (Na₂S₂O₅), L-cysteine and ascorbic acid.