Abstract: Background and Objective: Wastage of more than 90% cashew apples fruits can significantly be curbed, thus, this study evaluated the potentials of garlic-ginger filtrate as biopreservative compared with sodium benzoate and ascorbic acid in unpasteurized cashew apple juice. Materials and Methods: Unpasteurized cashew apple juices were pretreated with 1% garlic-ginger filtrate, 1% sodium benzoate (v/v) and 1% ascorbic acid (v/v). About 100% cashew apple juice served as positive control. All the samples were stored on the shelf at 26±2°C for 5 weeks. The pH, total titratable acidity, total soluble solids, specific gravity and enumeration of microbial load were done weekly. Results: The pH of garlic-ginger preserved unpasteurized cashew apple juice was relatively steady for 3 weeks. Garlic-ginger filtrate was the most effective preservative, followed by ascorbic acid and sodium benzoate, respectively without microbial and physiochemical deterioration for 3 weeks. Conclusion: Incorporation of garlic-ginger filtrate as biopreservative extended the shelf life of unpasteurized cashew apple juice at ambient temperature thus reducing the economic losses resulting from annual wastage and spoilage of the fruit.
INTRODUCTION
Cashew is a tropical fruit that is an essential component of a healthy balanced diet, but has short time frames of availability due to the climatic conditions of Nigeria1. Processing this fruit into juice reduces post-harvest loss though with short shelf life. About 90% of the harvested cashew apple is wasted and only 10% of the harvested cashew apple is either consumed fresh or industrially processed into a variety of products2,3. The shelf life of cashew apple juice is very short even when the juice is refrigerated. This affects the wholesomeness and quality of the cashew juice negatively leading to spoilage4. Sodium benzoate is broadly utilized as a food preservative and antimicrobial substance in industries, for products like jam, carbonated beverages, sauce, fruit juices and so on5. It impedes activities of micro-organisms by disrupting the membrane and repressing citrate cycle enzymes regardless of oxidative phosphorylation in fruit juice6. Despite the report of some adverse effects7, exceptionally low-level lethality has been recorded in mammals. Consequently, it is classified as a carcinogen-free substance8. Ascorbic acid known as Vitamin C is a natural compound of the family monosaccharide and it is soluble in water9. It is widely used as a preservative in food production due to its antioxidant ability and redox potential. It is consumed every day as a result of its medical advantages and inhibition of E. coli by ascorbic acid have been recorded by Usaga et al.10 in drinks. Biopreservation refers to extending the storage life and enhancing the safety of foods using natural compounds11. Ginger, the rhizome of Zingiber officinale is one of the most widely used species of the ginger family (Zingiberaceae)12. Ginger is a common ingredient in various beverages with medicinal values and also possesses a preservative effect due to its antimicrobial activity13. Garlic, known as stinky rose has antimicrobial activity on both Gram-positive and Gram-negative bacteria14. Besides its nutritional and medicinal values, garlic has been shown to have antioxidant potential15. Ginger and garlic are universally acceptable, relatively inexpensive and well tolerated by most people16. Juices are not only meant to quench people’s thirst, but offer essential nutrients for individuals. Spiced cashew juices can also play an essential part in the prevention of nutrition-related diseases by enhancing the physical well-being of the consumers hence functioning as a health drink17. The wastage of cashew apples had been attributed to short shelf life and rapid microbial deterioration18, hence the urgent need to inhibit spoilage and preserve cashew apple juice. This study assessed the microbiological changes during unpasteurized cashew apple juice production and preservation with reference to the inclusion of garlic-ginger (biopreservative), sodium benzoate (chemical preservatives) and ascorbic acid (chemical preservatives) for different samples.
MATERIALS AND METHODS
Materials: The study was conducted in Department of Microbiology, food processing and storage Laboratories in Landmark University (Latitude 8°9°0" N, longitude 5°61°0" E), Omu-Aran, Kwara state, Nigeria, between the period of March-July, 2017. Culture media products used from Oxoid, Basingstoke (England) namely nutrient agar, Man de Rogosa and Sharpe agar, Eosin methylene blue agar, MacConkey agar and Sabouraud dextrose agar. Sodium benzoate (LobaChemiePvt Limited, India) and Ascorbic acid (Nice Chemicals Private Limited, India) were used as chemical preservatives. Other chemical reagents were of analytical grade.
Methods
Experimental design: Three samples of cashew apple juice were pretreated with 1% sodium benzoate (v/v), 1% ascorbic acid (v/v), 1% garlic-ginger, respectively and 100% cashew apple juice served as positive control. All the samples were stored on the shelf at 26±2°C for 5 weeks.
Preparation of garlic-ginger filtrate: Fresh ginger rhizomes and garlic bulbs were procured from a local market in Omu-Aran, Kwara state, Nigeria. Fresh wholesome ginger rhizomes and the garlic cloves were washed under running water, peeled and separately diced into cubes. The diced cubes (50 g) weighed separately and blended with 50 mL of distilled water using a grinder (Marlex Appliances PVT, Mumbai, India) for 5 min. The suspensions were then filtered and the filtrates poured into labeled clean bottles. Garlic-ginger mix attained by mixing garlic and ginger at the ratio of 1:1 (v/v) and homogenized for 60 sec using a blender and transferred to a holding bottle.
Preparation of fresh unpasteurized cashew apple juice: The ripe and fully matured yellow variety of cashew apples, picked from 5 cashew trees at Landmark University orchard, Omu-Aran, Kwara state, Nigeria in March, 2017. They were placed into clean transparent plastic containers and transported immediately to the food processing laboratory. The cashew apples were cleaned using running tap water, drained in a colander, weighed and 10 kg of the apple expressed to obtain juice manually by squeezing/pressing for 20 min. The container for the collection of juice then covered with a muslin cloth. The unpasteurized fresh cashew apple juice was later divided into four aliquots of 1.0 L volumes, randomly aseptically transferred into different sterile conical glass jars and covered1.
Preparation of preserved cashew apple juice: Garlic-ginger filtrate (1% v/v), sodium benzoate (1% v/v) and 1% ascorbic acid (1% v/v) were added to cashew apple juice in respectively labeled containers. For easy identification ; CJ for 100% cashew apple juice without additive, CSB for cashew apple juice with 1% Sodium benzoate, CAA for cashew apple juice with 1% ascorbic acid and CGG for cashew apple juice with 1% garlic-ginger. The CJ served as a positive control. Aliquots (350 mL) from CJ, CSB, CAA and CGG were packaged in bottles, corked and stored for 5 weeks at ambient temperature (26±2°C). Collection of samples were carried out weekly from each bottle for analysis of physicochemical (acidity, pH, specific gravity and soluble solids) and microbiological changes (enumeration of the microbial population).
Determination of titratable acidity: Titratable acid of the samples was determined using phenolphthalein as an indicator of the endpoint by titrating 100 mL obtained by diluting 50 mL of juice with 50 mL of distilled water19 against 0.1 N NaOH.
pH determination: The pH meter (Jenway model 3310: Cole-parmer, Staffordshire, UK) calibrated with standard buffer 7.0, 4.0 and 9.2. Cashew apple juice (50 mL) was dispensed into a 100 mL beaker and the pH values were read and documented when equilibrium pH was reached19.
Determination of specific gravity: The specific gravity of each sample of cashew apple juice was determined by using a hydrometer (HB-Durac 61801, Novatech USA) by dipping the spindle into the different juices; water was used for rinsing the hydrometer after each reading. The readings were taken directly from the upper meniscus19.
Determination of total soluble solids: Four drops of cashew apple juice were placed on the refractometer (Hanna HI 96801, Hanna Instruments Inc., Woonsocket, RI, USA). The refractive index was read directly from the prism scale20.
Enumeration of micro-organisms in cashew apple juice: Following juicing, 10 fold serial dilutions (containing 1.0 mL of juice in 9.0 mL of water) of freshly prepared samples (1.0 mL) of CJ, CSB, CAA and CGG were used for enumeration of microbial populations over a range of ten (1010). The enumeration was repeated on weekly basis9,21,22. Nutrient agar was used for microbial enumeration for the total viable count, Man de Rogosa and Sharpe (MRS) for lactic acid bacteria count, Eosin methylene blue agar for the coliform count while MacConkey agar was used for enumeration of enteric bacteria. Culture plates incubated at 37°C and examined after overnight (20-24 h) incubation. Sabouraud Dextrose agar plates were used for enumeration of yeasts and molds incubated for 3 days at 28°C and examined.
Statistical analysis: Duncan Multiple Range Test (DMRT) was set at 5% level of significance to test for any significant difference and compare the level of effectiveness of chemical preservatives and biopreservative added to the unpasteurized cashew apple juice during storage across different treatments on all the parameter evaluated during the study. The means of the results obtained from all analysis conducted were calculated and separated by using MS Excel 2010.
RESULTS
Effect of preservatives on titratable acidity values: The total titratable acidity value of unpasteurized cashew apple juice without preservatives (CJ) and those preserved with sodium benzoate samples (CSB) were stable in the first one week (Fig. 1a) of storage. The unpasteurized cashew apple juice samples preserved with ascorbic acid (CAA) were relatively stable for 2 weeks (0.10) slightly decreased to 0.08 at the end of week 3 and later increased to remain at a stable value (0.11) for the remaining 2 weeks of storage. Bio-preserved unpasteurized cashew apple juice samples with garlic-ginger (CGG) total titratable acidity (0.06) were lower than CAA (0.11) at the end of storage for 5 weeks and this was significantly different.
pH values of preserved juices: Additions of sodium benzoate, ascorbic acid and garlic-ginger as preservative to fresh cashew apple juice have no significant effect on the pH values. There was a decrease in pH throughout the 5 weeks of storage in CJ while that of CSB was stable for 2 weeks followed by a decrease in the remaining storage period (Fig. 1b). However, the pH of CGG and CAA were stable for 3 weeks and later decreased.
Specific gravity during storage: The specific gravity of all samples either with or without preservative increased all through the storage period as presented in Table 1.
| Fig. 1(a-b): | (a) Total titratable acidity and (b) pH of unpasteurized cashew apple juice with 1% garlic-ginger, 1% sodium benzoate and 1% ascorbic acid during storage |
| Table 1: | Specific gravity of unpasteurized cashew apple juice at ambient temperature for 5 weeks |
CJ: 100% cashew, CGG: Cashew with 1% garlic-ginger, CSB: Cashew with 1% sodium benzoate, CAA: Cashew with 1% ascorbic acid, means followed by different superscripts are significantly different across columns at 5% level of significance (p<0.05) at the same storage time for different treatments and control | |
| Table 2: | Total soluble solid (°Brix) of unpasteurized cashew apple juice at ambient temperature for 5 weeks |
CJ: 100% cashew, CGG: Cashew with 1% garlic-ginger, CSB: Cashew with 1% sodium benzoate, CAA: Cashew with 1% ascorbic acid, means followed by different superscripts are significantly different across columns at 5% level of significance (p<0.05) at the same storage time for different treatments and control | |
The highest specific gravity was 1.67 recorded in CAA while CSB had the lowest value (1.32) at the end of the 5th week of storage.
Total soluble solid content: The total soluble solid content of CJ increased from 4.14-5.20°Brix all through the period of 5 weeks of storage. Addition of garlic-ginger filtrate to cashew apple juice significantly increased its total soluble solid to 5.03°Brix compared with CJ (Table 2), a slight increase to 4.22 and 4.20°Brix was also recorded in CSB and CAA, respectively at week 0. The total soluble solid of CGG was relatively stable for 4 weeks of storage while that of CSB and CAA increased for 2 weeks. The CGG was significantly different from CSB, CAA and CJ at p<0.05 after storage.
Effect of preservatives on the microbial load of cashew apple juice during storage
Total viable counts: There was no detectable microbial count in all freshly prepared cashew apple juices samples with or without preservatives at week 0. The total viable count of CJ gradually increased from 17×103 to 12×105 CFU mL–1 through the period of 5 weeks (Table 3). The total viable count of microbes in CGG remained constant (25×103 CFU mL–1) from week 2-3. This is contrary to the observation of the continual increase in the microbial total viable count across the 5 weeks in CJ, CSB and CAA.
Lactic acid bacteria counts: The Lactic Acid Bacteria (LAB) counts of CGG had no observable LAB growth in week 0 and 1.
| Table 3: | Total viable count (CFU mL–1) of unpasteurized cashew juice at ambient temperature for 5 weeks |
CJ: 100% cashew, CGG: Cashew with 1% garlic-ginger, CSB: Cashew with 1% sodium benzoate, CAA: Cashew with 1% ascorbic acid, means followed by different superscripts are significantly different across columns at 5% level of significance (p<0.05) at the same storage time for different treatments and control | |
| Table 4: | Lactic acid bacteria count (CFU mL–1) of unpasteurized cashew juice at ambient temperature for 5 weeks |
CJ: 100% cashew, CGG: Cashew with 1% garlic-ginger, CSB: Cashew with 1% sodium benzoate, CAA: Cashew with 1% ascorbic acid, means followed by different superscripts are significantly different across columns at 5% level of significance (p<0.05) at the same storage time for different treatments and control | |
| Table 5: | Yeasts and molds counts (CFU mL–1) of unpasteurized cashew juice at ambient temperature for 5 weeks |
CJ: 100% cashew, CGG: Cashew with 1% garlic-ginger, CSB: Cashew with 1% sodium benzoate, CAA: Cashew with 1% ascorbic acid, means followed by different superscripts are significantly different across columns at 5% level of significance (p<0.05) at the same storage time for different treatments and control | |
The LAB count of CGG was 34×103 CFU mL–1 after 2 weeks and increased until the 5th week (11×106 CFU mL–1). Ascorbic acid appears to have no effect as a preservative on the LAB population as CAA shared almost similar trend with CJ cashew juice in terms of LAB population (Table 4).
Yeast and mold count: Yeast and mold count were enumerated in all four samples and after one week, CJ, CSB and CAA had fungal growth except for CGG as shown in Table 5.
DISCUSSION
The decrease observed in CJ and CSB pH values were in agreement with Vwioko et al.23 and Ekanem and Ekanem24. The increase recorded indicates a decrease in acidity of the cashew apple juices coupled with having microbial and biochemical activities taking place together in the juice during storage25. Stability in pH values of CAA and CGG during storage suggested absence or undetectable microbial spoilage since high pH predisposes to microbial spoilage17. This might likely be the effect of added preservatives, which have resulted in improving the shelf life of the cashew apple juices in CAA and CGG. The total soluble solid content of the study was in agreement with Kaddumukasa et al.26. Increase in the total soluble solid content recorded in CJ was similar to that of Eke-Ejiofor27 during storage of orange juice. The results in this present study negated the observation of Vwioko et al.23, who reported that ‘sodium benzoate preserved soursop samples had the lowest microbial load than samples containing garlic-ginger’. This might be due to the insolubility of the powdery form of garlic ginger used for their study as reported by the authors. Mbajiuka et al.28 reported that garlic-ginger ethanolic extract had a significant impact on the shelf life of burukutu and reduced the incurred economic losses of brewers. The decrease in microbial load was reported during the storage of food products preserved with either ginger or garlic13,29. Physical, microbiological and biochemical changes peculiar to unpasteurized cashew apple juice provided in this study will serve as a benchmark for further research on utilization of cashew juice for industrial purposes.
CONCLUSION
Garlic-ginger filtrate added at 1% (v/v) as biopreservative effectively preserved unpasteurized cashew juice for 3 weeks without deterioration at ambient temperature. Garlic-ginger also showed proportionately superior preservative effect when compared with sodium benzoate and ascorbic acid during 5 weeks of storage at ambient temperature. Thus, the result proved that garlic-ginger filtrate could effectively serve as an alternative to chemical preservatives during the production of cashew fruit juice.
SIGNIFICANCE STATEMENT
This study discovered the application of ginger and garlic filtrate as biopreservative that can be beneficial for the preservation of cashew apple juice thereby minimizing its seasonal losses and wastage. This will improve income for the growers while boosting food security and nutrition, especially in developing countries. The insights provided in the current study will also create more in prospects for industrial exploration of cashew apple juice thus another product will be derived.