Effects of drying, packaging and storage on the quality and antioxidant properties of apple chips

The aims of the thesis were to identify changes on some quality and antioxidant properties of apple chips dehydrated at 65, 70 and 75°C produced from Starking Delicious (SD), Golden Delicious (GD) and Granny Smith (GS) apple cultivars, and packaged with two different packages during dehydration and storage. Moisture content (%), water activity, Polyphenol oxidase (PPO) enzyme activity, pH and titratable acidity, hydroxy methyl furfural content (HMF), ascorbic acid content, total phenolic content, total flavonoid content, total antioxidant activity (ORAC and TEAC), and Hunter L, a, b color parameters were determined at various dehydration stages. Phenolic compound analysis, sugar content, textural and sensorial analysis was carried out in all apple chips samples. The apple chips, received the highest score in sensorial evaluation, were packaged with a barrier and a non-barrier packaging materials. During storage, moisture content (%), water activity, ascorbic acid content, total phenolic content, total flavonoid content, total antioxidant activity (ORAC and TEAC), yeast and mold content, color parameters and textural properties were evaluated. Drying period of samples exhibited a declining trend. Midilli and Küçük model was the best model explained the drying behavior. Effective moisture ratio of samples increased with temperature and they were between 1.94-3.42x10-10 m2/s. Activation energy of different cultivars ranged between 51.02-53.07 kJ/mol.Water activity of all samples decreased during drying. Water activities of apple chips were between 0.17-0.19; 0.15-0.18; 0.15-0.18 for 65, 70 and 75°C temperatures, respectively.PPO enzyme activity detected in only fresh samples was the highest in SD cultivar and the lowest in GS cultivar. Titratable acidity and pH values were between 0.98-1.50 g/100 g d.w. (dry weight) and 3.51-4.46 for all samples, respectively. GS samples had higher titratable acidity and lower pH values and SD samples had lower titratable acidity and higher pH values than other samples. In analyzed samples, hydroxy methyl furfural content was between 0.39-8.62 mg/100 g d.w..Amounts of sucrose, glucose and fructose were 10.38-14,02; 10,99-17,46; 31,22-41,97 g/100g d.w. in fresh samples, respectively. Change in sucrose and glucose content was not significant.Initial ascorbic acid contents of fresh samples were between 15.7-16.3 mg/100 g d.w. Ascorbic acid content significantly decreased with drying. Thermal degradation of ascorbic acid was fitted to first order reaction kinetic. Total phenolic content increased with drying for all temperatures and cultivars. Total phenolic contents of apple chips were between 337-525 mg GAE/100 g d.w.. Changes on total phenolic content were fitted to first order reaction kinetic. Total flavonoid content increased during dehydration. Total flavonoid contents of apple chips were between 179-207 mg Catechin Equivalent/100 g kg d.w.. The change was fitted to zero order reaction kinetic. Activation energies were between 19.04-27.64 kJ/mol. The ORAC and TEAC values of samples increased during drying and they reached to the highest value in final products. ORAC and TEAC values of apple chips were between 9.25-15.41 and 12.27-17.97 mmol TE/100 g d.w., respectively. The change of ORAC and TEAC values were fitted to zero order reaction kinetic. Major phenolic compounds identified with HPLC of apple chips were gallic acid, chlorogenic acid, catechin, caffeic acid, epichatechin and rutin. Amounts of gallic acid, chlorogenic acid, catechin, caffeic acid, epichatechin were the highest in samples dried at 65°C.Color values changed relation to browning. While Hunter L values decreased, Hunter a and b values increased. Total color change was the highest at SD samples dried at 75°C temperature. Thermal change of total color change was fitted to first order reaction kinetic. In textural analysis of apple chips, breaking force were between 3,98-4,73 N. Based on sensory evaluation, apple chips produced at 75°C received the highest scores in respect to shape, odor, crispness, hardness, chewiness, sweetness, sourness, mild caramelize taste parameters. Apple chips from GS cultivar at 75°C temperature received the highest scores in respect to color, shape, crispness (in mouth), hardness, chewiness and sourness parameters.GS 75°C apple chips, received the highest scores in sensory evaluation, were packaged with barrier (PET/OPA/ALU/CPP) and non barrier (HDPE) packaging materials. Moisture content and water activities of samples with barrier packages were significantly lower than non-barrier samples. Barrier package protected initial moisture content and water activity of apple chips.Total color change was calculated as 2.74 and 2.95 for barrier and HDPE packages at end of storage, respectively. Breaking force is a textural property, increased during storage and it measured 4.80 N and 10.06 N for barrier and HDPE packages.The loss of ascorbic acid was 12.78 and 14.19% in barrier and non barrier packaged samples, respectively. Total phenolic content decreased during storage and changes were 7.45% and 7.19% for barrier and HDPE packages, respectively. Total flavonoid content decreased and it lost 14.56% in barrier packaged samples and 15.46% in HDPE packaged samples. ORAC values of apple chips decreased 7.32% and 8.80% for barrier and HDPE packages, respectively. While TEAC values increased 0.31% for barrier packaged samples, they decreased 0.67% for HDPE packaged samples.It was not observed yeast-mold growth for both packages during storage.