Process development and evaluation of tiger nut based chocolate products

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Dairy milk is a very versatile ingredient in the food industry because of its nutritional, sensory and functional properties. Increasing awareness among consumers about its associated allergies, concerns about its saturated fatty acids, scarcity and cost however have necessitated the development of plant materials as alternative food ingredients. The tiger nut tuber is a plant material that has been identified for the production of novel food ingredients for industry. The development of natural food ingredients of acceptable taste and quantity will however be important considerations in its use in industrial applications. Black and brown varieties of tiger nut tubers from eight different sites and planted in two different periods in Ghana were screened, and the milk extracted after optimizing process variables. The milk and cake were then analyzed and evaluated for their potential use in chocolate products. Proximate analysis showed that the average fat, ash, carbohydrate and fiber contents (g kg-1) of the black variety was 192.7, 14.3, 620.5, and 98.2, while that for the brown variety was 219.2, 16.0, 642.9, and 98.3 respectively. Carbohydrates and fiber contents ranged between 497.0 g kg-1 - 734.7 g kg-1 and 75.3 g kg-1 -135.4 g kg-1 respectively. Pre-treating equal weights of tubers from different sites by soaking and different combinations of soaking and cooking methods yielded significantly different results for the milk indices determined. Boiling of tubers before soaking showed higher milk yield (4395.5 g kg-1 to 6530.4 g kg-1) and milk solids (101.0 g kg-1 and 139.0 g kg-1) for all tubers. The results also showed significant differences in milk solids extracted from black and brown varieties with ranges of 541.4 g kg-1 to 619.4 g kg-1 and 571.4 g kg-1 to 710.2 g kg-1 respectively. In establishing the optimum conditions for milk solids extraction, the Response Surface Methodology (RSM) based on three (3) critical factors; milling time (X1), tuber: water ratio (X2) and boiling time (X3) was used. Regression analysis of the data indicated that the optimum extraction conditions for the black variety; was milling time, 17 minutes; meal: water, 1g: 6.4 ml; boiling time, 10 minutes and for the brown variety, milling time, 22 minutes; meal: water, 1 g: 7.0 ml; boiling time, 10 minutes. Under the experimental conditions, the yield of milk solids from the black tubers was 65.07 (0.40) % against the predicted value of 70.66 % while that of the brown cultivars was 74.84 (1.84) % against the predicted value of 80.99 %. The physico-chemical and functional properties of tiger nut milk, powder and cake were evaluated. The milk powder had protein content 76.9 ± 0.8 g kg-1, ash 24.4 ± 3.2 g kg-1, fat 395.6 ± 3.3 g kg-1, anti-oxidant content of 4634 ±17.0 mm frap/100g and total phenol of 187.7 ± 1.80 mg gallic acid equivalent/ml. The results also showed total sugars content of 353.7 ± 1.2 g kg-1, sucrose of 316.7 ± 1.5 g kg-1, reducing sugars 36.3 ± 1.0 g kg-1, bulk density 0.80 ± 0.02 g/cm3 and pH of 6.87 ± 0.02. The milk cake recorded water absorption capacity of 15.27 ± 0.16 ml /g, oil absorption capacity of 3.51 ± 0.21ml /g and total dietary fiber content of 559.7 ± 2.4 g kg-1. Quantities of sugar, cocoa powder, skimmed milk and tiger nut milk for chocolate beverage production were optimized using a four component constrained mixture design. A consumer panel evaluated appearance, mouthfeel, flavour, after taste and overall acceptability in the 15 formulations from the design. Regression models fitted to the data generated, and the optimum ingredient formulation for acceptable chocolate beverage was determined. The optimum ingredient formulations for acceptable tiger nut milk chocolate beverage were sugar, 20.56-28.58 %; cocoa powder, 8.73-19.67 %; skimmed milk powder, 5.0 % and tiger nut milk 54.77-60.50 %. The potential of tiger nut milk cake in bar chocolate and spread were also investigated. The ash, fat, protein and fiber contents of developed products increased with increasing substitution of sucrose and maltitol with the tiger nut milk cake. The observed trend from the sensory analysis for chocolate spread revealed that, increasing the proportion of tiger nut in the recipes resulted in a corresponding decrease in the ratings of the sensory attributes. An accelerated shelf life study showed that the beverage pasteurised at 70oC for 30 minutes and stored in Polyethylene terephthalate (PET) bottles at 18oC has a shelf life of 6 months. The physicochemical, functional and sensory properties of developed chocolate products indicated that processed tiger nut products may be considered as potential ingredient in beverages and high fiber diets.
This dissertation is presented in partial fulfillment of the requirements of PhD degree in Food Science and Technology, 2015