the effect of processing variables on the quality and ...

Journal of Food Processing and Preservation ISSN 1745-4549

THE EFFECT OF PROCESSING VARIABLES ON THE QUALITY AND ACCEPTABILITY OF PISTACHIO MILK jfpp_676

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AHMAD SHAKERARDEKANI1,2, ROSELINA KARIM1,3 and NAHID VASELI2 1 2

Department of Food Technology, Faculty of Food Science and Technology, UPM, Serdang, 43400 Selangor, Malaysia Department of Food Technology, Iran Pistachio Research Institute, Rafsanjan, Kerman, Iran

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Corresponding author. TEL: 00603-89468372; FAX: 00603-89423552; EMAIL: [email protected] Received for Publication April 28, 2011 Accepted for Publication December 21, 2011 doi:10.1111/j.1745-4549.2012.00676.x

ABSTRACT In an attempt to develop a new beverage from pistachio nuts, the effect of different methods of making paste, which involved grinding soaked kernels (method 1) and milling roasted kernels (method 2), as well as the blending time (20 or 30 min) and pH (6.5, 7.5 or 8.5) of the slurry on the pistachio milk compositions (protein, fat, total dry matter and total soluble solid), was evaluated. The taste and flavor of the pistachio milk were improved by the addition of sugar, vanillin and salt. The overall acceptability of the products was evaluated by 25 untrained panelists using hedonic test. The best processing conditions were milling the roasted kernels and blending the pistachio paste with water at pH 8.5 for 30 min. The most preferred flavor of pistachio milk is made by the addition of 5.0% sugar, 0.02% vanilla and 0.0% salt.

PRACTICAL APPLICATIONS This study describes a process for preparing pistachio milk from small-sized and unsplit pistachio nuts that cannot be used for direct human consumption. This product can be served as a substitute for animal milk.

INTRODUCTION Pistachios are one of the most nutritious nuts in the world. They contain dietary fiber, vitamin B6, thiamine, magnesium, calcium, phosphorus, copper, lutein, vitamin E, vitamin K, omega-3 fatty acid and phytosterol (Rainey and Nyquist 1997; Simopoulos 2002; Dismore et al. 2003; Simopoulos 2004; Heber and Bowerman 2008). Clinical and epidemiological studies have reported the beneficial effects of pistachio nuts to be the ability to decrease serum lipid levels, unhealthy cholesterol levels, coronary heart disease-related death, diabetes and gallstone disease (Rainey and Nyquist 1997; Kris Etherton et al. 2001; Jenkins et al. 2003; Sheridan et al. 2007; Heber and Bowerman 2008). Thus, there is a great potential for the food industries to develop various types of new products from pistachio nuts. One of the new products that could be developed is pistachio milk. It could be developed in countries that produce pistachio nuts for local consumption and export and could be consumed by lactose intolerant consumers. Pistachio milk can be used as a beverage like other vegetable milks or as a base for making other food products. Similar to the production of other vegetable milks, such as soy

milk, the production of pistachio milk involves soaking, milling, centrifugation, homogenization, clarification and pasteurization processes. Generally, soy milk is prepared by washing, soaking, dehulling and grinding the soy beans, followed by filtration of the slurry (Kamaly 1997). This procedure produces an undesirable bean-like taste in the flavor of the soy milk mainly due to the presence of volatile carbonyl compounds such as hexanal. Several attempts have been made to minimize this problem (Hashim and Chaveron 1995). Nelson et al. (1976) introduced the Illinois process for the production of soy milk whereby the bean-like flavor and the trypsin inhibitor are completely destroyed, and the efficiency of the extracted solid material and the protein were increased to 89 and 95%, respectively. Yazici et al. (1997) introduced a thermostable calciumfortified soy milk formula that contained soy flour (10%), sucrose (2.75%) and isolated soy protein (2.25%) added to water at 85–90C. Generally, heat treatments are applied to inactivate undesirable enzymes, such as lipoxygenase, and protein inhibitors, such as trypsin (Kumar et al. 2003), to gelatinize the starch

Journal of Food Processing and Preservation •• (2012) ••–•• © 2012 Wiley Periodicals, Inc.

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EFFECT OF PROCESSING ON THE QUALITY OF PISTACHIO MILK

A. SHAKERARDEKANI, R. KARIM and N. VASELI

and to denature 7S and 11S soy globins proteins (Zhang et al. 2004). Additionally, homogenization has been carried out in the soy milk production to improve the quality of the final product (Zhang et al. 2005; Lakshmanan et al. 2006; Cruz et al. 2007). Several studies have focused on the production of vegetable milk from nuts and seeds such as almond, peanut, sesame and rice (Lukaszuk et al. 2007). Jacques et al. (1997) described a process for the production of almond milk as a replacement for animal-based milk. The process of almond milk production includes heating partially de-oiled almond powder (~8%) at 90C and then grinding it, followed by centrifugation, sterilization (at an ultra-high temperature) and homogenization (Jacques et al. 1997). The composition of pistachio nuts are comparable to almonds, peanuts and sesame seeds as they contain water, protein, fat, carbohydrates and minerals (Shokraii 1977; Phillips et al. 2005; Venkatachalam and Sathe 2006; Alasalvar and Shahidi 2008). However, to date, no studies have been reported on the production of pistachio milk from pistachio nuts. Therefore, this study was undertaken with the following objectives: (1) to evaluate the effect of processing methods and variables (the method used to make the paste from the pistachio kernels, the blending time and the pH) on the chemical composition and physicochemical properties of pistachio milk, and (2) to study the effect of different formulations on the acceptability of the pistachio milk. FIG. 1. METHOD OF MAKING PISTACHIO PASTE

MATERIALS AND METHODS Pistachio nuts were supplied by the Iran Pistachio Research Institute. Citric acid, sugar, salt and vanillin were bought from Merck (Merck and Co., Whitehouse Station, NJ). In this study, pistachio paste was prepared using two different methods (i.e., variable 1). In the first method (Fig. 1), whole pistachio kernels were soaked in distilled water at room temperature (20 ⫾ 2C) for 4 h prior to the removal of the seed coat. The green kernels were ground into a paste using a mechanical grinder. In the second method, whole kernels were roasted at 110C for 20 min in a Memmert oven (Model UNB 500, GmbH, Schwabach, Germany). The roasted kernels were milled into a paste using a locally fabricated colloid mill. The paste from these two methods was blended in hot water (80 ⫾ 2C) in a ratio of 1:5 (nut : water) using a blender to produce the pistachio milk. Two blending times (i.e., variable 2) of 20 and 30 min were studied, and three different pH values (i.e., variable 3) for the slurry were used at pH 6.5, 7.5 and 8.5. The pH was adjusted with 0.5 N citric acid, and the slurry was filtered with a muslin-cloth. The pistachio milk was pasteurized at 70C for 30 s and stored at 4C before further analysis. The crude protein and fat content were analyzed using the Kjeldahl and Soxhlet, respectively (AOAC 1990). Infrared moisture balance (FD-610, Kett, Tokyo, Japan) and a 2

refractometer were used to analyze the moisture content and the total soluble solids (°Brix), respectively. The difference between the value 100 and the moisture content (%) was calculated as dry matter (Helrick 1990). All measurements were performed in triplicate. In the second part of the study, the best pistachio milk, based on its fat content, protein content, dry matter and total soluble solid, was used to produce flavored pistachio milk. The following ingredients were added to improve the taste and the flavor of the basic pistachio milk: sugar (5.0 and 6.0%), vanillin (0.0 and 0.02%) and salt (0.0 and 0.5%). A full-factorial design was used for making eight different formulations of flavored pistachio milk. The overall acceptability of the flavored pistachio milks was evaluated using the 9-category hedonic test by 25 untrained panelists. The scales used were like extremely (9), like very much (8), like moderately (7), like slightly (6), neither like or dislike (5), dislike slightly (4), dislike moderately (3), dislike very much (2) and dislike extremely (1).

Statistical Analysis A full-factorial design was used for this experiment. The results of the processing variables (the method used to make

Journal of Food Processing and Preservation •• (2012) ••–•• © 2012 Wiley Periodicals, Inc.

A. SHAKERARDEKANI, R. KARIM and N. VASELI

TABLE 1. EFFECT OF PROCESSING METHOD ON PROTEIN, FAT, DRY MATTER AND TOTAL SOLUBLE SOLID (TSS) OF PISTACHIO MILK

EFFECT OF PROCESSING ON THE QUALITY OF PISTACHIO MILK

Pistachio paste production

pH

Method 1*

6.5 7.5 8.5 6.5 7.5 8.5

Method 2†

Protein (%) b

Fat (%) b

TSS (°Brix)

c

5.0 5.2ab 5.4a 5.2bc 5.4b 5.8a

3.0 3.2ab 3.5a 3.2c 3.5b 4.0a

Dry matter (%)

2.7b 3.0ab 3.3a 3.4bc 3.6b 3.9a

9.5 9.9b 10.2a 9.8bc 10.0b 10.3a

Means followed by different letters within the column are significantly different (P ⱕ 0.05). * Method 1: soaked kernel was ground using a mechanical grinder. † Method 2: roasted kernel was milled using a colloid mill.

the pistachio paste, the pH and the blending time) were analyzed using analysis of variance. Comparisons between the means were performed using Tukey’s test (Minitab 15.1.1.0, Minitab Inc., State College, PA).

proteins and fats during blending. Based on the above finding, it can be deduced that the most suitable method for pistachio paste production was method 2.

Effects of pH Conditions

RESULTS AND DISCUSSION Effects of Different Methods of Making Pistachio Paste In this study, two methods for the production of the pistachio paste were used. In method 1, soaked pistachio kernels were ground to a paste with a mechanical grinder, whereas in method 2, roasted pistachio kernels were ground into a paste with a colloid mill. The pistachio paste was blended in water, and the effect of the pH of the slurry on the quality of the milk in terms of the amount of crude protein, crude fat, dry matter and total soluble solid contents was monitored. Table 1 shows that the amount of crude protein, crude fat, dry matter and total soluble solid contents is higher and significantly different in method 2 (P ⱕ 0.05). In this process, the pistachio kernels were ground into a fine paste using a colloid mill. All of the indigestible fibrous materials in the nuts were crushed and, hence, facilitated the release of all of the protein and fat components in the milk during blending. In contrast, all of the protein and fat contents of the milk produced using method 1 were lower, i.e., 3.5 and 5.4%, respectively, because the pistachio paste that was produced with a mechanical grinder (method 1) contained a substantial number of coarser particles that prevented the efficient extraction of the

TABLE 2. COMPOSITION OF PISTACHIO MILK AND COW’S MILK SAMPLE

Table 1 shows the influence of the pH values of the slurry during blending on the protein, fat, dry matter and total soluble solid contents of the pistachio milk.There was a significant increase (P < 0.05) in all of the variables monitored as the pH of the slurry was increased. The highest value of protein, fat, dry matter and total soluble solid content was observed in the pistachio milk that was processed at pH 8.5 using method 2. At this pH, the protein and fat content of the pistachio milk were 4.0 and 5.8%, respectively, because at this pH, most of the protein and fat contents were extracted and dissolved in water to form a stable emulsion. The mild alkaline condition causes the protein groups to ionize and, hence, create the negatively charged groups that resulted in electrostatic repulsion forces between the protein chains, which increases the protein solubility in water (Khalid et al. 2003; Osman 2004). When a comparison between commercial cow’s milk and pistachio milk samples at different pH conditions was made, it was observed that the pistachio milk processed using method 2 at pH 6.5 was comparable to cow’s milk and soy milk in terms of the protein and fat compositions, except for the total dry matter and soluble solids (Table 2). The total soluble solids increased with the increase in the pH values of the slurry. The increase in the °Brix of the pistachio milk from 2.7 to 3.3% using method 1 and from 3.4 to

Product Pistachio milk (Method 1*) Pistachio milk (Method 2†) Cow’s milk

Protein (%) b

3.0 3.2ab 3.4a

Fat (%) b

5.0 5.2a 3.5c

Total dry matter (%) c

9.5 9.8b 12.4a

TSS (°Brix)

pH

c

6.5 6.5 6.5

2.7 3.4b 12.4a

Means followed by different letters within the column are significantly different (P ⱕ 0.05). * Method 1: soaked kernel was ground using a mechanical grinder. † Method 2: roasted kernel was milled using a colloid mill. TSS, total soluble solid.

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A. SHAKERARDEKANI, R. KARIM and N. VASELI

3.9% using method 2 clearly reflected that the soluble solids were efficiently extracted during blending at pH 8.5. Other researchers have reported similar increases in protein extraction efficiency at increasing pH values (Shokraii and Esen 1988; Khalid et al. 2003). The amount of dry matter and the °Brix value of the pistachio milk using method 2 were 10.3 and 3.9%, respectively. The increase in the total dry matter and total soluble solids is due to the increase in the solubility of the proteins. However, the content of the total dry matter of the pistachio milk is lower than that of cow’s milk (Table 2). This issue can be addressed with suitable sweeteners, such as sugar, which will improve the taste of the final product.

Table 4. MEAN SCORES ON THE OVERALL ACCEPTABILITY OF PISTACHIO MILK MADE FROM DIFFERENT FORMULATIONS Formulation

Ingredients (%)

Mean score ⫾ SD

1 2 3 4 5 6 7 8

5.0 sugar, 0.02 vanilla, 0.0 salt 6.0 sugar, 0.02 vanilla, 0.0 salt 5.0 sugar, 0.02 vanilla, 0.5 salt 5.0 sugar, 0.00 vanilla, 0.0 salt 6.0 sugar, 0.00 vanilla, 0.0 salt 6.0 sugar, 0.00 vanilla, 0.5 salt 6.0 sugar, 0.02 vanilla, 0.5 salt 5.0 sugar, 0.00 vanilla, 0.5 salt

8.2 ⫾ 0.4a 7.8 ⫾ 0.8b 7.7 ⫾ 0.1b 7.6 ⫾ 0.1bc 7.5 ⫾ 0.1c 7.3 ⫾ 0.3cd 7.2 ⫾ 0.2d 7.0 ⫾ 0.4d

Means with different letters are significantly different (P ⱕ 0.05). SD, standard deviation.

Effects of Blending Time The effects of different blending times on the quality of the pistachio milk produced from the pistachio paste made using method 2 were studied (Table 3). The results showed that the blending time had a significant (P < 0.05) influence on the content of protein, fat, dry matter and total soluble solids of the pistachio milk. Increasing the blending time from 20 to 30 min increased the protein content and the total soluble solids significantly. Based on the above findings, it can be deduced that the most suitable pH values and blending times for producing pistachio milk using method 2 were pH 8.5 and 30 min, respectively.

quality of pistachio milk. The recommended method for producing paste is method 2, which involved grinding the roasted pistachio kernels using a colloid mill. The most suitable blending time and pH condition were 30 min and 8.5, respectively. Based on the hedonic test, the most preferred flavored pistachio milk was made by adding 5.0% sugar, 0.02% vanilla and 0.0% salt.

ACKNOWLEDGMENT The authors would like to thank the Iran Pistachio Research Institute for the financial support.

Overall Acceptability of Pistachio Milk The overall acceptability of eight different formulations of flavored pistachio milk samples was evaluated using the hedonic test. All of the formulations were acceptable to the panelists. The mean score ranged from 7.0 to 8.2, which are “moderately like” to “like very much.” The most preferred product was formulation 1, which comprised 5% sugar, 0.02% vanilla and 0.0% salt (Table 4).

CONCLUSIONS The results from this study indicated that the method of making pistachio paste, the pH condition and the blending time of the slurry are important variables that influence the TABLE 3. EFFECT OF BLENDING TIME ON THE COMPOSITION OF PISTACHIO MILK MADE USING METHOD 2* Time (min)

Protein (%)

Fat (%)

Dry matter (%)

TSS (°Brix)

20 30

4.0b 4.4a

5.8ab 6.0a

10.3ab 10.5a

3.9b 4.4a

Means with different letters within the column are significantly different (P ⱕ 0.05). * Method 2: roasted kernel was milled using a colloid mill. TSS, total soluble solid.

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