Development and Quality Evaluation of Choco Quinoa Nutri Bar during Storage

Choco quinoa nutri bar was developed using quinoa as one of the ingredients to explore its nutritional benefits. Bars were packed in polypropylene (PP, 75 µ) and metallised polyester (12 µ) low density—high density (MP, 100 µ) (with/without vacuum) films, stored under ambient and 37˚C temperature conditions for shelf life evaluation. Bar contained 14.43% protein, 14.93% fat with a calorific value of 426.75 k cal/100g. Chemical changes were observed significantly (p < 0.05) more in the samples stored at 37˚C than the ones stored at ambient conditions (15˚C - 34˚C). Bars showed maximum stability at 0.33 a w with less chemical changes. Oleic acid (36.06%) was found to be the major fatty acids in the bar followed by palmitic (29.35%), stearic (17.12%) and linoleic (12.05%) acids. Hardness of the bar enhanced significantly during storage, and was observed significantly (p < 0.05) higher in the samples packed in MP films (with/without vacuum) as compared to bars packed in PP films thus restricting the shelf life of the bar to 6 months in MP films (with/without vacuum) and 9 months in PP films at both the temperature conditions.


Introduction
Quinoa (Chenopodium quinoa Wild) is referred to as a pseudo-cereal, produces seeds of pale yellow colour, but may vary from white through pink, orange or red to brown and black [1]. Quinoa is rich in its nutritive value, with remarkable protein content and its protein nutrient is comparable to that of milk protein [2] In the present study, quinoa has been used as one of the ingredients due to its high nutritional value along with the other ingredients viz cocoa powder, cocoa butter, raisins, nuts etc. for the preparation of choco quinoa nutri bar and evaluated for its oxidative stability by packing them in polypropylene (PP), Metallised Polyester (MP, with and without vacuum), storing them at ambient (15˚C -34˚C) and 37˚C temperature conditions.

Materials and Methods
The ingredients used in the preparation of choco quinoa nutri bar consist of quinoa crispies obtained from M/s Quessentials Pvt Ltd, Ananthpur. Whey protein concentrate, procured from M/s Strategic Marketing and Research, Bengaluru. Cocoa powder (Cadbury brand), cocoa butter, raisins, oats (Baggery brand), liquid glucose and almond obtained from local market of Mysuru.
All the chemicals and solvents used in the present study were of analytical reagent grade.

Methods
Moisture, fat, protein and total ash contents were estimated as per the standard methods of AOAC (1984) [8]. Peroxide value, free fatty acids as well as fatty acid profile were estimated by the method of AOCS (1990) [9]. Total sugar was estimated as per the method described by Khan [13]. Microbiological analysis of bar was carried out as per the method of APHA (1992) [14].

Measurement of Browning Index
Browning intensity (OD) in choco quinoa nutri bar was carried out as per the method of Khan et al. [15] by shaking 5 g of powdered bar sample with 70:30 ethanol/water for 2 h and measuring optical density at 420 nm.

Effect of aw on Lipid Peroxidation
The effect of water activity (a w ) on lipid peroxidation was determined by keeping 120 g samples in desiccators for 40 days at ambient temperature (15˚C -34˚C) containing phosphorous pentoxide to obtain 0.0 water activity (a w ) and saturated solutions of magnesium chloride, sodium bromide, sodium nitrate and barium chloride to obtain water activities (a w ) of 0.33, 0.57, 0.73 and 0.90 respectively.
Initially and periodically at an interval of 10 days, stored samples were analysed for moisture, peroxide value, free fatty acid value, thiobarbituric acid value and antioxidant activity.

Texture Analysis
The firmness of the sample as shear force was measured using a texture analyser (TA HD Plus, Stable Micro Systems, London, UK) equipped with 50 kg load cell and extended craft knife operated at a test speed of 5 mm/sec. Firmness was the maximum force recorded on the chart in kg. The data obtained from texture profile analysis were used for determining the toughness and shear value.

Sensory Evaluation
The sensory characteristics of samples were evaluated in terms of colour, aroma, taste, texture and overall acceptability using a 9 point Hedonic scale, grading 9

Results and Discussion
Analysis of proximate composition of choco quinoa nutri bar ( Quinoa has an excellent amino acid balance with higher lysine (5.1% to 6.4%) and methionine (0.4% to 1.0%) contents [18] [19] [20]. Hence, in order to explore the beneficial effects of this wonder pseudocereal, quinoa in the form of crispies has been incorporated in the preparation of a bar and the amino acid amino acid lysine was also found to be present in fairly good amount (561.01 mg/100g). Bar showed 388.90 mg/100g of threonine and other essential amino acids were found between the range of 110 -181 mg/100g. L-Aspartic acid was found in higher amounts (596.26 mg/100g) among the non-essential amino acids identified in the bar followed by L-Alanine (301.50 mg/100g) and L-Proline (308.40 mg/100g). L-Cysteine was found in a very meagre amount i.e., 30.01 mg/100g in the bar.  Lipid oxidation is one of the important processes that occurs in most of the food systems and a major cause of food deterioration during processing and storage [21]. In the present study, the extent of lipid oxidation of choco quinoa nutri bar has been monitored by studying the changes that took place in peroxide value (PV), free fatty acids (FFA), thiobarbituric acid (TBA) and browning index (BI) during storage at ambient (15˚C -34˚C) and 37˚C temperature conditions in different packaging materials (    Texture is a critical sensory attribute which determines the quality of a food and is related to the deformation, disintegration and flow of a food when a force is applied on them [22]. In the study, texture of choco quinoa nutri bar was described using toughness and work of shear by measuring the cut force ( Sensory acceptance of choco quinoa nutri bar was assessed by studying the changes in terms of colour, aroma, taste, texture and over all acceptability (OAA) scores during storage at ambient and 37˚C temperature conditions in different packaging materials (Table 5). Significant (P < 0.05) differences were  The bars packed in PP films scored slightly better value for texture, may be due to the slight sogginess of a bar with slightly more moisture which facilitated easy bite from the panellists as compared to the bars stored in MP films (with and without vacuum). Figiel and Czopek (2006) [23] has also reported a significant decrease in hardness of a candy, when there was an increase in moisture content by 0.5 units. Vacuum packing of bars also aided in enhancing the hardness, as vacuum packing of dry cured ham in multilayered laminated film has resulted in increased hardness, cohesiveness etc when samples were stored for 8 weeks as compared to the non vacuum stored samples [24]. The development of tough or hard texture in protein rich bar may be attributed to the thiol-disulfide interchange reactions during storage, which leads to cross linking, aggregation and network formation [25] [26]. Surface hydrophobicity and more ordered secondary structure of protein can also cause hardening during storage [27]. Initially bar received an OAA score of 8.17 on a 9 point hedonic scale which decreased significantly (p < 0.05) to a lower value of 6.41 in samples packed in MP films under vacuum at 37˚C followed by MP alone which scored 6.60 under same temperature conditions. The next lowest value was observed for the samples stored under ambient (15˚C -34˚C) conditions, which scored an OAA score of 6.83 and 6.75 when packed in MP films with out and with vacuum respectively. Since lower limit for the acceptability of the product was considered as 7 on a 9 Point Hedonic scale, the bars packed in PP films was found acceptable for 9 months, while the samples packed in MP films (with and without vacuum) remained stable for 6 months only under both the temperature conditions. The effect of water activity (a w ) on lipid peroxidation of choco quinoa nutri bar at a w levels of 0.0, 0.33, 0.57 and 0.73 during 40 days of storage at ambient conditions (15˚C -34˚C) are represented in Figure 3. The initial moisture content of the bar was 6.87%, changed significantly (p < 0.05) to 0.38, 4.73, 7.80, 11.27 at 0.0, 0.33, 0.57 and 0.73 a w levels at the end of 40 days of storage. Significant (p < 0.05) decrease in moisture content was observed at 0.00 and 0.33 a w , while samples kept at 0.57 and 0.73 a w levels showed a significant (p < 0.05) increase in their moisture content during storage. Samples stored at all a w levels attained equilibrium in their moisture contents after 30 days of storage and remained almost constant thereafter till the end of the study.  respectively, at the end of 40 days of storage at ambient conditions. At 0.33 a w, both PV and FFA showed slower increase from 3.66 to 20.21 meq O 2 /kg fat and 1.87% to 3.50% oleic acid, thus indicating the maximum stability of the product at 0.33 a w . The stability of the bars at 0.33 a w may be attributed to the formation of hydrogen bonds between water and peroxides which prevent the decomposition of hydroperoxides. Also, water hydrates transition metal ions thereby reducing their activity to decompose hydroperoxides [28]. The results obtained from our study are in conformity with published data [28] [29]. The increase in FFA may be due to the hydrolysis of fats in the presence of water, and followed the same trend as that of PV at different a w levels.
Antioxidants are the compounds which inhibit the process of lipid oxidation by reacting with the radical formed from fat to form a stable radical, which do not quickly react with reactive oxygen, thereby extend the shelf life of processed foods by protecting them against deterioration [30]. It is evident from the  Microbiological analysis carried out in choco quinoa nutri bar ( Figure 4) at regular intervals of time, revealed no microbial counts. The samples were found free from yeast and mold counts and SPC count was found within the acceptable limit during the entire storage period.

Correlation Analysis
The chemical changes like PV, FFA, TBA and browning observed during storage was found to be negatively correlated (r ≥ −0.99) with over all acceptability . It was observed from the study that, correlation between the chemical changes and OAA for the samples stored under 37˚C was not varied much with that of ambient conditions, because the chemical changes that took place at both the temperature conditions, though observed significant, but not affected the sensory quality in terms of OAA which was clearly revealed by sensory panellists. As far as the texture of the bar is concerned, the texture was found to be po-

Conclusion
A highly nutritious bar can be prepared with the incorporation of quinoa to enhance its protein quality. Bars stored at 37˚C underwent deterioration at a slightly faster rate as compared to the bars stored at ambient conditions. Packing in vacuum films was not found beneficial in extending the shelf life of the bar.
Even though bar remained chemically, sensorily and microbiologically safe during the entire storage period, increase in the hardness was found to be the limiting factor for the acceptability of the bar thus restricting the shelf life to 6 months in the samples packed in MP films (with/without vacuum) and 9 months in PP films under both the temperature conditions.