Analysis of quality attributes of Hibiscus sabdariffa ( zobo ) drinks blended with aqueous extract of ginger and garlic

Various types of highly valued food and medicinal products are produced from Hibiscus sabdariffa in different parts of the world. In Nigeria, the calyces of this plant are processed into a refreshing nonalcoholic beverage known as zobo. In this work, zobo drink was prepared using hot water extraction method and the juice obtained was blended separately with aqueous extracts of ginger and garlic. Physico-chemical, microbiological and sensory properties of the various blends of zobo were investigated. The results of this study showed that the zobo samples contained different concentrations of ascorbic acid which ranged between 22.5 and 35.8 mg/100 g. The pH ranged between 3.94 and 7.67, while the total sugar was between 2.5 and 3.56 mg/100 g. The samples also contained varying concentrations of Mg 2+ , K + , Ca 2+ , Fe 2+ , Na + and Zn 2+ . The total viable counts of the samples during storage showed that the microbial loads increased steadily and ranged between 1.2 × 10 3 and 3.7 × 10 7


INTRODUCTION
Hibiscus sabdarffa belongs to the super order Malvaceae and it is believed to originate from East Africa (Ilondu and Iloh, 2007).H. sabdariffa plants are cultivated and consumed as vegetable and tea, whereas other Hibiscus varieties are planted for the fibres they produce.It is called different names like Roselle and Sorrel in English and it is locally called zobo and Isapa in Nigeria (Adebayo-Taye and Samuel, 2000).
Many parts of Roselle including seeds, leaves, fruits and roots, are used in various foods.Among them, the fleshy red calyces are the most popular (Yadeng et al., 2005).Roselle is used in many folk medicines.In Nigeria, the dry red calyces are processed into a refreshing nonalcoholic beverage known as zobo.Despite the fact that the popularity of zobo juice is increasing, one of its greatest limitation for large scale production is that it has a very short shelf life of 24 h if not refrigerated (Omemu et al., 2006).Therefore, there is urgent need to explore various preservation methods that could be employed to extend the shelf life of this product.Dougheri et al. (2007) employed some chemical preservatives to improve the shelf life of zobo drink.They reported that only samples treated with benzoic acid remained organoleptically attractive after 14 days of storage.However, the problem with the use of chemical preservatives in food is that they tend to have adverse effects on the health of consumers (Adesokan et al., 2010).Therefore, naturally occurring plant extracts with proven antimicrobial properties will be preferred in food preservation (Kolapo et al., 2007).The use of natural preservatives has become more popular as compared to synthetic antimicrobials and antioxidants (Aliu et al., 2007).
Ginger (Zingiber officinale) and garlic (Allium sativum) are two plants traditionally used as spices in food preparation but have been demonstrated to have both antioxidant and antimicrobial activities (Kolapo et al., 2007).Therefore, the objective of this present study was to evaluate the physico-chemical and microbiological qualities of zobo drinks blended with ginger and garlic extracts.

Collection of samples
Dry calyces of H. sabdariffa and fresh wet form of ginger rhizomes and garlic bulbs were obtained from local Bodija market in Ibadan, Nigeria.The samples were manually cleaned by handpicking stones and other unwanted debris.The samples were then thoroughly washed separately using sterile de-ionized water and allowed to air dry under the sun (40°C).

Preparation of ginger and garlic extracts
One hundred grams of each of the spices were separately chopped into small pieces with a clean stainless steel knife.The chopped spices were then blended into 50 ml de-ionized water with a Kenwood blender having stainless steel blades until smooth pastes were obtained.The pastes were diluted further with 100 ml deionized water and filtered using a clean Muslin cloth.The resulting extracts were stored in clean bottles inside a refrigerator (5°C) until needed for use in zobo preparation.

Preparation of zobo drinks
For hot extraction, 175 g of already cleaned calyces of H. sabdariffa was added to 300 ml hot boiling water and was left to stand for 15 min.The hot, red-coloured aqueous extract was filtered with the white muslin cloth into a plastic bowl and tightly covered.The resulting zobo juice was separately blended with ginger, garlic, ginger/garlic mixtures at different concentration of 2.50 and 10%.The unblended zobo juice served as control.

Physico-chemical analysis
The pH of the zobo samples was measured by using a standardized pH meter (Micron pH meter).Appropriate procedure of A.O.A.C. (1990) was used to determine the metallic ion contents.Flame photometry was used to determined sodium, potassium and iron and Buck scientific atomic absorption spectrophotometer (model 200A) was used to determine calcium, magnesium and zinc.Crude protein and total sugar content was also estimated (A.O.A.C., 1990).

Microbiological analysis
The various zobo drink samples were serially diluted in sterile distilled water and appropriate dilutions were plated on nutrient agar, potato dextrose agar (PDA) and MacConkey agar for total viable, fungal and coliform counts, respectively.The nutrient and MacConkey agar plates were incubated at 35°C for 24 h, while the PDA were incubated at 28°C for 72 h and were supplemented with streptomycin to inhibit the growth of bacteria (Adesokan, 2005).

Sensory analysis
The blended zobo samples were analyzed by a 10 member panel that are familiar with the product which comprises of the students of the Polytechnic, Ibadan.The samples were scored based on a nine point hedonic scale where 1 equals extremely like and 9 equals extremely dislike.The data obtained were subjected to analysis of variance (ANOVA) and the means were separated by Duncan multiple range test (Kolapo et al., 2007).

RESULTS
The physico-chemical analyses of the various blends of zobo beverages are presented in Table 1.The result showed that the ascorbic acid content (mg/100 g) increased gradually and its values ranged between 22.5 in pure zobo juice (Sample A) and 35.8 in zobo/ginger/garlic mixture (Sample D).The pH values increased steadily and ranged between 3.94 in sample A and 7.67 in sample D. The total sugar also ranged between 2.5 and 3.56% in sample D. The result also indicated that the zobo samples blended with spices had higher crude protein contents than non-spiced zobo beverage and it values ranged between 9.1 (Sample A) and 62% (Sample D).
The various blends of zobo drink contained varying concentrations of Mg 2+ , K + , Ca 2+ , Fe 2+ , Na + and Zn 2+ .Another finding of this study is that the zobo beverages extracted with hot water had higher amount of nutrients than the sample extracted with cold water (result not shown).
The total viable counts (TVC) (cfu/ml) of the zobo samples are presented in Table 2.This result showed that there was a progressive increase in TVC with storage time.However, the zobo samples containing ginger or garlic had lower (P≤0.05)TVC than zobo samples containing no spice.Sample A had the highest count of 3.7 x 10 7 cfu/ml, while sample D had the lowest count of 2.6 x 10 4 cfu/ml by the seventh day of storage.The organoleptic properties of the beverages are presented in Table 3 and the result indicated that sample D had the highest overall acceptability of 2.3, while sample A had the lowest value of 1.9.

DISCUSSION
This work demonstrated that the ascorbic acid contents of zobo drinks supplemented with garlic and ginger are higher than that of ordinary zobo juice.This means that the vitamin C status of zobo beverages can thus be improved by blending with these spices.Babalola et al. (2001) reported the presence of ascorbic acid in various varieties of H. sabdariffa.The pH of the zobo samples blended with ginger and garlic are higher than that of the zobo juice which contain no extract.This implies that zobo juice is slightly acidic and should not be consumed without snack or on an empty stomach.A recent study revealed that the pH of the fruit flavoured zobo drinks had a low value which ranged between pH 2.19 and 3.62 (Fasoyiro et al., 2005).
The crude protein content of non-spiced zobo juice was 9.1% but higher values were obtained for the samples containing spices.This means that the spices are rich in protein.The crude protein value is similar to the one obtained by Olayemi et al. (2011).The zobo drinks evaluated in this work contained various metallic ions like Mg 2+ , K + , Ca 2+ , Fe 2+ , Na + and Zn 2+ .Olayemi et al. (2011) also reported various concentrations of these metallic ions in three different varieties of zobo subjected to the same preparation condition.In addition to this Builder et al. (2010), reported the presence of certain phytochemicals like alkaloids, saponin, tannin, phenols, sterols, etc.
The spices used in this study were able to reduce the microbial loads of zobo samples during the seven days storage.However, Ogiehor et al. (2008) extended the shelf life of zobo for 42 days using 0.2% ginger extract and refrigeration.This method of storage under refrigeration is not practicable in present day Nigeria because of epileptic public power supply and the use of power generators is not economical.The sensory attributes of the zobo samples containing spices were also enhanced.The use of extracts of ginger and garlic in zobo preparation should therefore be encouraged as the sensory properties and shelf life of resulting product will be enhanced.

Table 1 .
Physico-chemical properties of different blends of zobo drink.Sample A, Unspiced zobo beverage; sample B, zobo with ginger; sample C, zobo with garlic; sample D, zobo with ginger and garlic.**Values are means of three determinations. *

Table 2 .
Total viable counts (cfu/ml) of the different zobo blends during storage.

Table 3 .
Sensory evaluation of different blends of zobo drink.