Analysis of quality attributes of banana drinks blended with aqueous extracts of ginger

This study aimed to investigate the effect of ginger (Zingiber officinale) on the microbiological, physicochemical and sensory quality of banana (Musa spp .) drink. Production of banana juice was achieved with hot and unheated water extraction. The various juices obtained were supplemented with aqueous extracts of ginger in concentrations of 2.5 and 10%, stored and analyzed periodically for microbiological and physicochemical (pH, vitamin C, proteins, total sugars, Mg, k, Ca, Fe, Na, Zn) characteristics. The results showed that ginger addition to either hot or unheated banana juice extraction treatment significantly reduced growth of microorganisms as reflected in total viable counts from day 4 of storage. Vitamin C, proteins and mineral contents increased as compared to control samples. The results of this study suggest that the incorporation of ginger extracts into banana drink could be an effective means of preserving banana drinks.


INTRODUCTION
Plantain is one of the primary sources of food product intended for consumption in Côte d' Ivoire.It is the second food crop in Côte d' Ivoire with an annual production of 1.6 million tons.Its main production area is the midwest (ANADER, 1998).
Although it occupies a prominent place in the diet of Ivorian, production of plantain remains seasonal.This seasonality is characterized by a period of relative abundance (October to March) where post-harvest losses are high.During this period, the sales prices are low and another period of shortage in urban markets (April-September) marked by the high cost of banana and inaccessibility of the product for low income households.
Thirty to forty percent of this production is unfortunately lost before consumption, mainly due to poor harvest, transport and storage (Lépengué, 1999).Indeed, these losses are due to storage of bananas at room temperature (28-35°C) than the recommended 8-12°C (Varoquaux et al., 2002) temperature, the remoteness of production and lack of accessible roads to urban areas.Moreover, not processing or very low level of transformation of plantain is an obstacle to the develo-pment of the plantain sector in Africa in general and in Côte d'Ivoire in particular.
Thus, "the production of plantain juice clarified and stabilized" will not only help reduce post-harvest losses but also offer a new product that will improve the income of the plantain industry.However, the juice of plantain like that of Hibiscus sabdariffa (zobo) (Omemu et al., 2006) has a shelf life of not more than 24 h if not refrigerated.
To solve this problem of conservation, Dougheri et al. (2007) have used benzoic acid thus extending the shelf life of zobo (a drink made from the calyces of Hibiscus subdariffa) to 14 days.They were able to preserve the same the organoleptic qualities beyond 14 days.However, the use of these chemicals has various negative effects on the health of consumers (Adesokan et al., 2010).In this regard, Kolapo et al. (2007) preferred natural plant extracts with antimicrobial properties.The aim of the present study was to determine the effect of ginger (Zingiber officinale) on microbiological, physicochemical and sensory quality of fruit juice of plantain (Musa spp.)

Sampling
Plantain variety "Corne" and the roots of ginger (Z.officinale), were purchased at market Guro Adjamé (Abidjan) in Côte d'Ivoire.These samples were carefully sorted and manually washed with bleach, then rinsed thoroughly with distilled water before use.

Ginger juice extraction
One hundred grams of ginger roots were cut into small pieces with a sterile knife.The ground material obtained is then mixed in 50 ml of distilled water using a "Kenwood blender" having cutting blades until a fine paste.The paste is dissolved in 100 ml of distilled water and filtered through a muslin cloth.The filtrate is stored in sterile bottles in a refrigerator at 5°C until use (Adesokan et al., 2010).

Banana juice production
A cold and hot water extraction methods were performed.For both methods, 500 g banana pulp were dispersed in 1 L of distilled water in a blender brand "Phillips" .The resulting mash was filtered using a sieve of 0.250 mm diameter.The filtrate was then centrifuged at a speed of 4000 rev/min for 30 min with a centrifuge brand Heraeus Christ, Bofuge III.Residues separated juice was placed in a sterile bottle and ginger juice added at different concentrations (2.5 and 10%).Juice of plantain non-supplemented ginger served as controls.

Physicochemical analyses
Measurement of pH at 25°C was done for each day for 15 days using a pH meter, according to AOAC (1990).Proteins were determined by Kjédhal method (BIPEA 1976).The dosage of Anderson et al. 261 vitamin C was produced according to the AFNOR method (1995).Mineral elements: iron, potassium, calcium, magnesium, sodium, copper, zinc, manganese were determined by atomic absorption spectrophotometer according to the method of AOAC (1990) and Abulude et al. (2007).

Microbiological analyses
The various banana juices were carefully diluted in sterile distilled water.Appropriate dilutions were poured onto agar PDA (potato dextrose agar) and MacConkey respectively for the enumeration of total coliforms and flora.Boxes cast in MacConkey medium were incubated at 35°C for 24 h while those of PDA medium were incubated at 28°C for 72 h and supplemented with streptomycin to prevent bacterial growth (Adesokan, 2005).

Sensory analysis
Different extracts of banana juice were analyzed by a panel of 17 people previously formed by the Ivorian society of Tropical Technology (I2t).The samples were evaluated on a scale of 0 to 10.

Statistical analysis
STATISTICA 10 software was used to perform statistical analyses.
Comparisons between the dependent variables were determined by analysis of variance and Duncan's test and Newman Keuls.Statistical significance was defined at 5%.The results for sensory tests were subjected to analysis of variance using the software Tastel +

RESULTS
The physicochemical analyzes of the various plantain drinks are shown in Moreover the results indicate that the lowest protein content (0.25%) is that of the sample C0 while the highest content 0.65% is that of cold extraction treatment supplemented with 10% ginger.Plantain drinks contain varying concentrations of Mg 2+ , K + , Ca 2+ , Fe 2+ , Na + and Zn.The sample F10, that is, the cold water extract treatment containing 10% ginger has a higher concentration than the other juice samples.The enumeration of the total flora, expressed in cfu/ml of various banana juice samples are summarized in Table 2.
These results show that there is a steady increase in the total flora with time of storage.However, the samples    fortified with ginger contain less germs than the controls.After seven days of storage, the sample F0 contain the highest flora (7.10 cfu/ml), while the lowest (4, 9.10 cfu/ml) quantity is contained in the C10 sample.
The organoleptic properties of plantain juice are shown in Table 3 and these results indicate that the cold extract F2 has the highest overall acceptability of 5.4, while the cold extract sample F10 has the lowest acceptability (3.2).

DISCUSSION
At the end of this study, it is clear that vitamin C content is higher in the different juices supplemented with 2.5 and 10% ginger extracts.This shows that the vitamin C level can be improved by ginger addition.This assertion seems justified by research conducted by Adesokan et al. in 2005 who indeed improved the ascorbic acid content of the juice "ZOBO" through the use of mixtures of ginger and garlic in fresh or powder forms.The pH value of banana juice was increased with increasing ginger concentration.This implies that plantain juice with more acid should not be used when the stomach is empty.Proteins content also increases with the content of ginger.These show that ginger improves protein content as in the study of Adesokan et al. (2005) and Olayemi et al. (2011).Different plantain drinks characterized in this study have varying contents of metal ions such as Mg 2+ , K + , Ca 2+ , Fe 2+ , Na + and Zn 2+ .A study by Olayemi et al. (2011) on three different "zobo" drinks showed variations in their mineral contents following spices incorporation.Similar results were revealed by Adesokan et al. (2005) study in the "zobo" drinks supplemented ginger.
In addition, we found that ginger extract can reduce the total flora of plantain juice during 7 days of storage.The presence of mono and sesquiterpenoids within the ginger extracts is considered main cause of their antimicrobial activity (Bajpal et al., 2009).The mode of action of these compounds involves cell walls and cell membranes attacks affecting their permeability and functions (electron transport, nutrient uptake and enzyme activity).
These results are in agreement with those of Adesokan et al. (2005) andOgiehor et al. (2008) who were able to maintain the quality of "zobo" drink for 42 days by combining refrigeration and ginger (0.2%) addition.

Conclusion
From this work, it can be concluded that ginger provides mineral fortification and antimicrobial benefits to banana drink during storage for 7 days.Therefore, it is suggested that ginger could be used to extend the shelf life of fruit juices, which seems more healthful than synthetic additives.The ginger extracts showed an interesting antimicrobial activity and could therefore be used to preserve various food products.The extracts may find application in antibacterial and antifungal therapies.Additional research is needed to elucidate mechanisms of action of bioactive molecules in the extracts.

Table 1 .
Contents of proteins, total sugars, minerals, vitamin C and pH of banana juice supplemented with ginger extracts.

Table 2 .
Total viable counts (cfu/ml) of the different banana drinks during storage.
d Sample codes are as stated in Table 1.Values are means of three replicates.

Table 3 .
Sensory evaluation of different banana drinks.