Improving the qualitative indicators of apple juice by Chitosan and ultrasound

Abstract Today's consumers desire for tasty, nutritious, and safe food products, so researchers are looking for new ways in which little heat or no heat at all is used for processing. This study was to evaluate the effect of treatment using an ultrasonic bath (for 15, 30, and 60 min at 40 and 60°C) and ultrasonic probe (for 10, 15, and 20 min at 40 and 60°C), treatment with Chitosan, and combination of them on the quality of apple juice that includes physicochemical features (pH, acidity, total solid matter), total polyphenol, total antioxidant capacity, the cloud point, and color values of Hunter (L*, a*, b*) in the treated samples and comparing them with each other. The results showed that ultrasound has no effect on the pH and acidity, while the total solid of ultrasound treatment was higher than controls in combination with Chitosan (p < 0.05). Total polyphenols of apple juice samples treated by ultrasonic probe are higher than an ultrasonic bath (p < 0.05). The total antioxidant capacity has improved in treatments (p < 0.05). According to the results there is a significant difference between the cloud point of control samples and Chitosan (p < 0.05). The L* (brightness) increased in ultrasonic probe method and had a significant decline in Chitosantreatment (p < 0.05). Findings from this study suggest that the use of ultrasound treatment in the production of apple juice can improve quality factors, and in this regard, ultrasonic probe is more effective.

application of ultrasound in the food industry is a useful and attractive tool due to high efficiency, short time, easy, cost and energy saving, a method of "eco-friendly" as defined in Ashokkumar et al. (2008) and Castro Domingues et al. (2012). Ultrasound equipment in laboratories is either baths or ultrasonic probe. Ultrasonic bath is economically affordable, and handling equipment can be easily carried out. The other type of ultrasound equipment is ultrasound probe that has a higher intensity and power because the material is applied at the micro level, and electrical failure occurs less frequently because probe is placed directly into the reaction vessel.
The aim of this study was to evaluate the effect of treatment by ultrasound (bath and probes), treatment with Chitosan alone, and the combination of ultrasound treatments (bath and probe) and Chitosan on the quality of apple juice containing features like physicochemical (pH, acidity, total solids), total polyphenol, total antioxidant capacity, the cloud point, and Hunter color values (L*, a*, b*) in the treated samples and to compare them with each other.

| Ingredients
Yellow apple variety of Golden Delicious was purchased from the market. Reagents and chemicals were prepared from Merck (Darmstadt, Germany) and consumption solvent was prepared from Barcelona, Spain, with the highest purity.

| Preparation of apple juice
Fresh apples were purchased from the local market. Apples were washed with water, dried with paper towels, and then were cut into four pieces with a stainless steel knife, while seeds and stems were separated from the apples. Apple juice was extracted using a domestic juice and was smoothed using a cleaning cloth. Control samples were tested in order to the pasteurization at 71°C for 6 s and stored in the refrigerator (Abid et al., 2013).

| pH
pH was measured at 20 ± 0.5°C. pH meter was calibrated with a solution of a commercial buffer 4 and 7 (Abid et al., 2013).

| Titratable acidity
Ten milliliter of the sample was poured into 250 ml of the beaker, and 90 ml of distilled water was added. The solution was titrated with a profit of 1/N to the endpoint of pH = 2.8 ± 0.1. Titratable acidity was obtained from the following equation (AOAC, 1999):

| Total polyphenol content
The total content of phenolic was carried out using two methods of spectrophotometry and Folin-Ciocalteau. Gallic acid was used as a standard (Boyer & Liu, 2004).

| Total antioxidant capacity
Apple juice total antioxidant capacity was measured in accordance with a procedure done by Oboh and Ademosun (2012). Ascorbic acid was used as standard, and the antioxidant capacity was measured compared to it.

| The cloud point
The procedure was done with a little modification in accordance with the Versteeg, Rombouts, Spaansen, and Pilnik (2006).

| Color
Sample color was analyzed using a colorimeter at Hunter Laboratory. The device was calibrated with white reference. Color values were read in terms of CIE L* a* b* system that L* is (white or light to dark ratio), a* (red-green ratio), and b* (yellow-blue ratio) (Abid et al., 2013).

| Statistical analysis
Statistical analysis of treatments was carried out by the analysis of variance (ANOVA) using SPSS 16 software. A significant difference between means was determined at 0.05 by Duncan test.

| Determination of pH, acidity, and total solids changes
The effect of ultrasound and Chitosan on pH, acidity, and total solids (Brix) of apple juice samples is shown in Figures 1-3. There was no difference between the pH and acidity of ultrasound treatments (bath and probe) and controls (p > 0.05). The pH and acidity of the samples treated with Chitosan had no significant difference with combination of ultrasound + Chitosan treatment (p > 0.05).
These results are consistent with the findings of Walkling-Ribeiro, Noci, Cronin, Lyng, and Morgan (2009) that observed no significant effect of combined treatment of electric pulses and ultrasound on pH, acidity, and total solid contents of orange juice. The findings of Abid et al. (2013) also showed that ultrasound does not cause significant changes in pH, acidity, and total solid content in apple juice.
Results obtained by Tiwari, Patras, Brunton, Cullen, and O'Donnell (2010) did not show significant differences in the pH, acidity, and total solids during grape juice ultrasound treatment. pH of Chitosan samples was higher than control and ultrasound (p < 0.05). This effect can be attributed to the nature of poly cationic Chitosan that has a linking property with acid and excluded acidic compounds from the environment. Data from the survey of Chitosan and ultrasound on the total solids of apple juices showed that samples treated with ultrasound are higher in total solids than the control (p < 0.05).
The total amount of solid material samples treated with Chitosan and ultrasound + Chitosan treatments have higher total solids than other treatments (control and ultrasound), respectively (p < 0.05).

| Assessment of total polyphenol and total antioxidant capacity changes
The     for the increase of these compounds. All these results suggest that ultrasound of apple juice is beneficial for consumers from a commercial standpoint and from the standpoint of nutrition.
According to the results presented in Figure 5, there is a significant difference between the treatments (p < 0.05). The total antioxidant capacity of ultrasound and ultrasound + Chitosan treatments was higher than control.
This finding is similar to the findings obtained by Abid et al. Oszmianski and Wojdyło (2007) reported that Chitosan has no effect on antioxidant activity of apple juice, and our results are similar to their findings. So that the ultrasound treatment increased the total antioxidant capacity of apple juice samples; however, Chitosan had no effect on the total antioxidant activity of apple juice (p < 0.05).
An increase in temperature from 40 to 60°C and the ultrasonic probe were more effective in increasing total antioxidant capacity (p < 0.05). Increase in total antioxidant capacity can be because of increase in ascorbic acid and phenolic compounds resulting from cavitations over the ultrasound of apple juice that increases extracting such compounds. Polyphenolic compounds have a high antioxidant capacity.

| Determination of cloud point and color changes
The results obtained about the effect of ultrasound and Chitosan on the cloud point and color (L*, a*, b*) is shown in Figures 6-9.
According to the results, there is a significant difference be- Unwanted particle deposition in apple juice due to the ultrasound treatment is likely responsible for the increase in L*. Tiwari et al. (2008) reported that an increase in the amount of L* is probably due to an

| CON CLUS ION
Findings from this study suggest that the use of ultrasound treatment in the production of apple juice can improve the quality factors, and in this field, ultrasound probe is more effective than ultrasound bath. The ultrasound treatment significantly improves the phenolic compounds, total antioxidant capacity without affecting the physicochemical parameters of pH and acidity of apple juice. The cloud point and chroma Hunter in samples treated with ultrasound have improved compared to Chitosan. Therefore, it is suggested to use new technology of ultrasound to improve the quality of apple juice from the standpoint of the consumer health. However, further research is needed to determine the effect of ultrasound on the sensory and functional properties of apple juice.

ACK N OWLED G M ENT
The authors thank research fellows at food science laboratories in the Standard Research Institute of Iran and Sari Agricultural Sciences and Natural Resources University for their technical assistance.

CO N FLI C T O F I NTE R E S T
None declared.

E TH I C A L S TATEM ENT
This work does not involve any human or animal studies.