Development of Cassava mahewu in Powder of Instantaneous Reconstitution

: Mahewu is a traditional cool non-alcoholic fermented beverage known among African countries; generally made from cereals but also it can be made from tubes. The raw material (cereals and tubes) is spontaneity fermented at room temperature by acid lactic bacteria, the fermentation process is considered to increase the nutritional content of mahewu . The beverage is most known in the liquid form, that takes up more volume and less shelf life. The presentation of mahewu in powder it will allow minor volume and increase the shelf life. The objective of the present study was to develop cassava mahewu in powder form in order to stabilize a protocol of rehydration and investigate its instantaneous behavior. The standard cassava mahewu was prepared using fermentation techniques and thereafter 30 g and 40 g were firstly frozen for 24 h/-18°C followed by freeze drying at -20°C for a period of 24 h to obtain the powder form of cassava mahewu . The pH and acidity levels were controlled throughout the preparation processes and the total solids content of the solution was adjusted to 15.9 ± 0.1 ºBrix, in order to freeze dry with a quantity of known soluble solids. The moisture content, water activity (w a ), tests of instantaneousness (wettability and dispensability) of the powdered cassava mahewu and the sensorial properties of the reconstituted powder after rehydration with water at 25°C to replace 60%, 80% and 100% of water lost during the freeze-drying were evaluated using standard methods. The results showed a reduction of the pH (6.11 to 4.56) and an increased in acidity (0.06 g/100g to 0.25 g/100g of lactic acid) of the standard cassava mahewu at beginning (t = 0 h) and at end of fermentation (t = 24 h) respectively. Both samples of 30 g and 40 g indicated a water activity of 0.39 and 0.42, moisture content of 6.50 and 8.57% and instantaneousness of 3 s and 3.33s respectively. The results showed an optimal behavior of instantaneousness of 3 s indicating an easy penetration of liquid (water) on the powdered cassava mahewu . According to the sensorial analysis, the reconstituted cassava mahewu rehydrated with 100% of water lost during the freeze drying was more appreciated and preferred compared with 80% and 60%.


Introduction
Mahewu is a non-alcoholic fermented beverage known and produced in larger scale in Southern African region.It is consumed as food and cool drink in this region and also normally used as weaning food for children between 4 to 8 months [1,2].In general, mahewu is rich in nutrients resulting from the process of fermentation, which influence positively the digestion and absorption of nutrients in the human body [3].The fermentation process leading to the formation of mahewu is due to the action of Lactic acid bacteria (LAB), which offer extension of shelf-life, increases the nutritional value and improve the organoleptic characteristics (such as taste, aroma and texture) of the mahewu [4,5].Moreover, fermented products including mahewu have been reported to have health benefits such as prevention of diarrhea infections in children, improvement of immune system and prevention of cancer diseases [6].
In Africa mahewu is traditionally made mainly from cereals such as maize, rice and millet as well as tubers namely sweet-potatoes [7] and cassava [8].The mahewu from maize is the most popular, which in Mozambique has been produced in commercial scale and called "super mahewu" [9].Among the African countries, Zimbabwe is known as the most producer of maize mahewu followed by South Africa and Botswana [10].Recently in Mozambique cassava mahewu has produced and it is considered an alternative to other mahewu produced from other carbohydrate extracts [8].
Mahewu is well known in the liquid form presentation, though maize mahewu in powder for instantaneousness reconstitution has been produced at commercial scale in Zimbabwe using spray dry or drum dry techniques [11].However, in Mozambique research about the development of mahewu from maize or from cassava in powder has not yet been developed.In this context, the intent of the present study was to develop cassava mahewu in powder form using freeze drying process and instantaneously reconstitute it as the liquid cassava mahewu being developed by Salvador et al., [8].The success of the present purpose will allow the extension of shelf-life of cassava mahewu by decreasing the metabolism of LAB and practically stops the fermentation process.According to Hofuendahl and Hahn-Haherdal [12], the optimal temperature for the LAB activity for mahewu fermentation varies from 20 to 45°C.

Experimental Design
The present study followed three principal experimental steps shown on the Figure 1.

Cassava Mahewu (Standard/Original) Preparation
Cassava mahewu was prepared according to the method developed by Salvador et al., [8] Figure 2. The cassava flour for mahewu preparation was acquired from Zama-Zama farmer association at Inhambane Province, Mozambique.During the mahewu preparation, samples of 10 mL were taken and thoroughly homogenized for pH measurement at the beginning (t = 0 h) and at the end of fermentation (t = 24 h) using the method described by Brasil [13].Other 10 mL of samples also were taken at the beginning and at the end of fermentation for titratable acidity where 2 to 3 drops of phenolphthalein indicator were dropped then titrated with 0.1 N of sodium hydroxide solution under constant agitation [13].The balance was reached by the change of color to pink after 30 seconds as result of the presence of the indicator.The titratable acidity was express as percentage of lactic acid according to the formula below.% = 0.1 * * * 0.9 ℎ The soluble solids were measured at 20°C using a Digital Abbe WAY-S refractometer (Cometa Selecta group, Barcelona Spain) at the beginning and at the end of fermentation, where 10 g of cassava mahewu standard/original samples properly homogenized was placed to the prism.The result was express in °Brix [14], one Brix (1°Brix) correspond to 1 g of sugar per 100 g of solution or 1% of sugar.The water activity of cassava mahewu at the end of fermentation was read directly at 20°C using Aqua Lab water activity meter S 3TE (Pullman, Washington, USA) [15].

Preparation of Cassava Mahewu in Powder Form
Cassava mahewu prepared on 2.2 was sweetened by adding sugar then subjected to freeze drying process in order to obtain the cassava mahewu in powder form according to Gonçalves [16].The 30 g and 40 g of cassava mahewu previously prepared were placed in disposable glasses, frozen at -20°C during 24 h, then transferred to flask of 300 mL, the flasks were taken to freeze drying machine at approximately -20°C for a period of 24 h for dehydration to obtain cassava mahewu in powder as illustrated on the scheme Figure 3.

Parameters Analyzed in the Cassava Mahewu in Powder
To the cassava mahewu in powder obtained, the following parameters were analyzed: moisture content, water activity, instantaneousness properties and sensorial analysis.

Determination of Moisture Content and Water Activity
The moisture content was determined according to Normas Analíticas do Instituto Adolfo Lutz [15]; where 10 g of cassava mahewu in powder was placed to oven at 105°C to dry directly; the value of moisture content was found when the weight was constant.The water activity was determined as described previously on the liquid cassava mahewu (2.2).

Evaluation of the Instantaneous Behavior of Powdered Cassava mahewu
The instantaneousness of cassava mahewu in powder was divided in two parameters: wettability and dispensability.To determine the wettability, 2 g of cassava mahewu in powder was weighed in a beaker with 400 mL of distilled water at 25°C and the period of time taken was measured using digital timer and the time was reached when all particles were visibly wet [17].In the dispensability determination, 26 g of cassava mahewu in powder was placed in the beaker with 200 mL of distilled at 25°C then thoroughly mixed for 15 seconds.For the evaluation of performance of powder suspension after mixing, the following criteria were used: i) Poor -when the majority of powder is in suspension; ii) regular -minor part of powder in suspension; iii) goodsome particles of powder in suspension and iv) optimal for the absence of particle of powder in suspension [17].

Evaluation of the Sensorial Properties of Powdered Cassava mahewu
The sensorial analysis was made to evaluate the acceptability and the intention purchasing of the cassava mahewu in powder.This was performed by the workers of Sumol + Compal enterprise constituted by 30 testers of different ages and social classes [18].The acceptability test was made obeying a hedonic scale of 1 to 9 points, where the extremes positive and negative were 9 equals to like it a lot and 1 equal to dislike it a lot and 5 was the middle and equal to did not like or dislike.The acceptability evaluation was followed by the test of the intention of purchasing, evaluated based on 4 parameters namely: would certainly buy; probably buy; probably not buy and certainly not buy.

Cassava mahewu in Powder Rehydration
(Reconstitution) The rehydration of cassava mahewu in powder where made by replacing 60%, 80% and 100% of water removed during the freeze drying.After rehydration of cassava mahewu in powder (reconstituted), the sensorial analysis was performed based on multiple comparison in order to evaluate the level of difference between cassava mahewu in liquid form (original/standard) and cassava mahewu in powder (reconstituted) with 60%, 80% and 100% of water removed on dehydration.For the evaluation, a portion of 16 mL of each sample of rehydrated cassava mahewu was served to the testers in codified transparent plastic glasses together with the control sample also codified; and mineral water was used to clean the plate between served samples.Fifteen (15) trained testers of different ages and social classes constituted by workers of the enterprise Sumol + Compal participated in the evaluation; all participants were informed about the objective of the study in order to decide their participation or not and informed consent was signed.Before the evaluation the participants were oriented and the test obeyed a scale from 1 to 5 points as follow: none-difference (1), minor difference (2), moderate difference (3), very different (4) and extreme difference (5).After the identification of level of difference between the rehydrated cassava mahewu in powder and the control, the sample which was more approximated to the control was applied the hedonic scale of 1 to 9 points; where the extremes positive and negative were 9 equals to like it a lot and 1 equal to dislike it a lot and 5 was the middle and equal to did not like or dislike in order to evaluate the acceptability of cassava mahewu in powder reconstituted.The acceptability of cassava mahewu in powder was calculated based on the index of acceptability (IA) [19] IA (%) = (A/B) x 100; where A = to the average of the results of the acceptability test and B = major score obtained on the acceptability test for each parameter.

Data Analysis
The data was analyzed using the analysis of variance (ANOVA) to calculate the significant differences between treatments.The separation of means was activated using the Tukey test with level of significance of 95%.The tests were applied to see the difference between different parameters (pH, acidity and soluble solids) during fermentation of cassava mahewu, variation of water activity, moisture content and wettability.

Variation of pH, Titratable Acidity, Soluble Solids of Cassava mahewu Standard/Original in Function of Fermentation Time
During the fermentation process there was decreases on pH and soluble solids and increasing of acidity.There was significant difference (p<0.05) in pH and titratable acidity at the beginning (t = 0 h) and at the end of fermentation (t = 24 h); and no significant difference was observed in soluble solids (p>0.05),Table 1.The results of the present study were similar with the observations of Salvador et al. [8].This observation is attributable to the proliferation of microbial population during the fermentation time.The decreases of pH on cassava mahewu can provide security against pathogenic bacteria and also extend the shelf-life of the product.Annan et al. [20] reported the importance of acidity developed in fermented products to avoid bacteria growth and prevention for diarrhoea infections.The soluble solids were decreased due to the use of carbohydrates as energy source by the fermentative bacteria [21].

Variation of Water Activity and Moisture Content on Cassava mahewu (Standard/Original) and Cassava mahewu in Powder
Table 2 shows the variation of moisture content and water activity of cassava mahewu and cassava mahewu in powder after freeze drying.Logically, the decrease of moisture content and water activity on cassava mahewu in powder when compared to cassava mahewu standard can be seen.The results in Table 2 are in agreement with the requirement for powder products showing the efficacy of freeze-drying process on dehydration of cassava mahewu in powder.The water activity of cassava mahewu in powder was below 0.6 which according to Chisté et al. [22] is the minimal limit for the development of microorganisms.This makes the cassava mahewu in powder suitable for consumption and storage with good characteristics.The moisture content of cassava mahewu in powder was different from the dehydrated powder [13], but within the requirements.The difference on the moisture content can be explained by the difference in the quantity of samples freeze dried.

Instantaneous Behavior of Cassava mahewu in Powder
The instantaneousness properties (wettability and dispensability) of cassava mahewu in powder shows no significant difference between cassava mahewu freeze-dried at 30 g and 40 g respectively.The values show optimal behaviors of wettability and dispensability for cassava mahewu in powder which can be seen on Table 3.The cassava mahewu in powder presented lower period of wettability (3 s) indicating the ease penetration of liquid on the cassava mahewu in powder.The cassava mahewu in powder is poor in fat taking into account the content of fat in cassava estimated in 0.1% [23]; this fact made the cassava mahewu in powder more hydrophilic thus influencing the wettability and dispensability [24].When compared to products with higher contents of fat such as milk powder which was reported to have period of wettability and dispensability grander than 60 s and others [25,26].

Rehydration of Cassava mahewu in Powder
From 30 g of cassava mahewu 6 g of cassava mahewu in powder was obtained, meaning that 24 g corresponded to the water content withdrawn during dehydration by freeze drying process.Figures 4 and 5 presents the differences between cassava mahewu in powder rehydrated at 100% (replacement of 100% of water withdrawn) with cassava mahewu (standard/original) and the general classification of the cassava mahewu in powder rehydrated.It can be seen (Figure 4) that 80% of taster's responded that there is no difference between cassava mahewu in powder rehydrated at 100% and cassava mahewu (standard/original); however, 20% says that there is slight difference.The Figure 5 shows the acceptance of rehydrated cassava mahewu in 100%, the categories with highest percentage were liked it (46.7%)and liked it a lot (26.7%).For the cassava mahewu in powder rehydrated at 80%, the tasters (20%) found huge difference between the rehydrated cassava mahewu in powder at 80% and cassava mahewu (standard/original) and 53.3% of tasters responded to have moderated differences (Figure 6).About 33.3% of taster responded to have extreme difference between cassava mahewu rehydrated at 60% and cassava mahewu (standard/original) and 60.0% of taster responded to have considerable difference Figure 7.Among the different proportion (100%, 80% and 60%) of rehydration cassava mahewu in powder, the rehydration at 100% was closer to the cassava mahewu standard/original when compared to the rehydration at 80% and 60%.It can be noted that during the rehydration of cassava mahewu in powder, when less amount of water was added the result was different to the characteristic of the cassava mahewu standard/original making the cassava mahewu more consistent/dense due to less water, distorting their characteristics in relation to the cassava mahewu standard/original.In general, the heaviness of these two proportions (80% and 60%) justified the negative evaluation by the tasters.The findings of the present study are similar of the study developed by El-Bachá & Kim [27] who reported that the samples hydrated at 100% as closer to the standard.The results of this study are also supported by Ratti [28] who reported that the freeze-dried products are easily rehydrated.The factor of the cassava mahewu in powder rehydration at 100% being closer to the standard/original indicates that the freeze drying was well succeeded, as was able to remove water, maintained the pores to the cassava mahewu in powder in order to receive again water during the rehydration.

Evaluation of Acceptability and Purchase Intention
The attributes of acceptability of cassava mahewu in powdered form was fundamentally concentrated in more than 95% of punctuation of hedonic scale liked from slightly to really enjoyed, the best values were liked a lot (33.7%) and really enjoyed (46.7%).For the color attribute, the acceptability index was 90% and for the texture, the obtained an acceptability index was 86.7% and 100% of punctuation in the hedonic scale of liked starts slightly to very much.The aroma attribute received 96.7% of the punctuation in the hedonic scale liked started from slightly to really enjoyed, where liked a lot got 23.3% and really enjoyed 46.7% with the index of acceptability evaluated in 88.9%.The attribute flavor obtained 96.3% of acceptability index, concentrated 100% on the hedonic scale liked started from slightly to really enjoyed where liked a lot was 16.7% and really enjoyed 76.7%.The cassava mahewu in powder was accepted with index of acceptability varied from 86.7 to 96.7 for all attributes evaluated (color, flavor, aroma and texture) which are superior to the minimal acceptability index estimated in 70% [29].
The global impression of cassava mahewu in powder got an acceptability index equal to 89.5%, indicated that it was well accepted taking into account the results of evaluation where 100% of hedonic scale fallen in liked varied from slightly liked (40%) to really enjoyed (33%).All taster says that they would purchase the cassava mahewu in powder, being 83.3% affirmed that surely purchase and 16.7% probably purchase; these statements coming to substantiate the possibility of marking cassava mahewu in powder as the results of the present study differed to Souza & Rodrigues [30] who considered their product as marking with 66% of surely purchase.Table 4 shown the parameters which could be used to prepare cassava mahewu in powdered form, that can be rehydrated to replace 100% of water lose during the freezedrying process.The standardization of cassava mahewu in powder proposed in the present study allows the extension of the shelf life and better storage of cassava mahewu.

Conclusions
There was no significant difference between cassava mahewu in powder rehydrated at 100% and cassava mahewu standard/original.The cassava mahewu in powder developed in the present study showed good acceptability and could be considered instantaneous and easily reconstituted.A protocol for cassava mahewu in powder which could be used to prepare cassava mahewu in minor volumes with higher shelf life was developed in the present study.The powder of cassava mahewu could be considered a convenient product as can be consumed at any place and time due to its instantaneously and portability.The development of cassava mahewu in powder form using other technologies (such as spray dryer) is recommended.

Figure 3 .
Figure 3. Flow chart of cassava mahewu in powder preparation.

Table 1 .
Variation of pH, titratable acidity, soluble solids of cassava mahewu (standard/original) in function of fermentation time.

Table 2 .
Variation of moisture content and water activity of standard cassava mahewu with powdered cassava mahewu.

Table 3 .
Instantaneous behavior of cassava mahewu in powder.