Sensory Properties and Microbial Characteristics of Cookies Prepared from Refined Wheat Flour Supplemented with Sweet Potato Flour and Whey Protein Concentrate

A study was conducted for sensory analysis and microbial assay for the cookies supplemented with refined wheat flour, sweet potato flour and whey proteins concentrate (WPC-80). The cookies made were nutritious Sensory evaluation for microbial study conducted Results from sensory analysis revealed that all treatment combinations are in acceptable level. Among all, T 3 HT1 (20% SPF and 20% WPC) best in overall acceptability. The SPC ranges from 1.400±0.548 to 4.400±0.548 from 0 th to 30 th days, Yeast and mould was NIL in 0 th and 15 th day on 30 th it Coli forms count is NIL 0 th th 30 th for different treatment


INTRODUCTION
The sweet potato Ipomoea batatas (L.) belongs to the Convolvulaceae. Sweet potato is among the world's most important and under-exploited crop [1]. Sweet-potato (Ipomoea batatas L) is the seventh most important food crop in the world. It is grown in many tropical and subtropical regions. Among the world's major food crops, sweet-potato produces the highest amount of edible energy/ha/day [2]. Sweet-potato flour can serve as a source of energy and nutrients (carbohydrates, beta-carotene (pro-vitamin A), minerals (Ca, P, Fe, and K), and can add natural sweetness, color, flavor, and dietary fiber to processed food products. Because of the distinct properties, the use of sweet-potato flour in the preparation of bread is restricted; Biscuits are baked dry products, usually with a golden brown crust and crispy texture [3].
Whey was previously considered as waste because of its potential for spoilage. Now days however it is no longer considered as a waste product but treasure of nutritionally rich whey proteins. WPC has many health benefits and clinical importance. WPC is useful in the treatment of various diseases and health problems such as cancer and high cholesterol [4]. It is effective in trauma, burn and renal failure [5,6]. It has the ability to act as antibacterial and antiviral agent [7]. Whey proteins are easily and readily digested and therefore useful in post operative care of patients. Its use is beneficial in diabetes, cardiac ailment, liver problem, arthritis, gout and antihypertensive. It is antitumor agent and giving antioxidant effect [8,9]. WPC has immune-enhancing property due to which it can be used in treating HIV patients. Whey protein also acts as a sport, food as whey proteins helps in speedy repairing of injured and torn muscle during practice and performance [10,11]. Whey proteins provide excellent nutritional values in nutrition, foods formulated for infant, kids, adults and old aged people as growth tonic for body health maintenance.
Bakery industry in India is considered as one of the major food processing industry with an annual demand of over 2758 MT [11]. (Ministry of Food Processing Industries, 2013). India is known to be the second largest manufacturer of biscuits, first being USA. Bakery products are the most popular food consumed by all age groups and are gaining popularity as processed foods because of their availability, ready to eat convenience, and comparatively good shelf life.
As discussed above, it is clear that sweet potato flour is rich in dietary fiber, functional fiber. Whey protein concentrate is rich in available protein content, high calcium and minerals, it can be considered as fortification for plain cookies.

MATERIALS AND METHODS
Sweet potatoes were procured locally from the field after harvesting. Roots were washed, trimmed and cured to make them free from soil and other foreign materials, rotting, insect damage and washed with common salt and made into slices, dried by using a tray drier at 60°C for 6 h and then Grinding, Sieving on 70 mesh [2]. The prepared Sweet potato flour Packed in HDPE and stored for 6 months or more in sealed containers.
WPC were procured from Mahan proteins ltd., Delhi, India. Refined wheat flour, sugar, shortening (Amul Butter) were procured from local market of Allahabad (India) and kept at room temperature for further use. All chemicals used were of analytical grade.

Preparation Dough for Cookies
The dough was made in a laboratory mixer. Fat and sugar was creamed in a mixer with a flat beater for 2 min at slow speed. Sodium chloride was added to the resulting cream, and mixed for 5 min at high speed to obtain a homogeneous mixture. Finally, flour containing various proportions of sweet potato flour, and whey protein concentrate (WPC-80), which had been sieved twice with baking powder was added, and mixed for 3 min at medium speed. The dough preparation, sheeting and moulding followed by different heat treatments like baking at 180°C for 15 mins, microwave heating at 180°C for 10 mins and frying at 180°C 8 mins. Combination treatment with different heat treatments is given in the following

Sensory Evaluation
The evaluation was done by 5 trained and semi trained panelists at Warner College of Dairy Technology, SHUATS. Judgments for developed cookies were made through rating products on a5 point Hedonic scale [12]. With corresponding descriptive terms ranging from 5 'like extremely'

Microbial Analaysis
Standard plate count, Yeast and mould and Coli form were determined by using serial dilution pour plate method. The number of colonies appeared on dilution plates were counted, averaged and reported as cells per gram (cfu/gm) of the sample.

Statistical Analysis
To determine the statistical significance of sensory and microbial evaluation of cookies were analyzed using minitab18 software by ANOVA followed by Tukey's test (one-way) at a 5% significance level. All values are expressed as mean and standard deviation of five parallel measurements.

Sensory Properties of Different Types of Cookies
Organoleptic evaluation offers the opportunity to obtain a complete analysis of various properties of food as perceived by human senses. Sensory evaluation is an important and best method for evaluating the organoleptic properties of various products which provide quality measure and production control. To select the sensory attractive cookies prepared by different combinations of sweet potato and whey protein concentrate (WPC-80), were subjected to sensory evaluation using 5 point hedonic scale. Colour and appearance , body and texture ,flavor and taste, mouth feel and over all acceptability were the parameters studied for selecting the better product among the different treatment combinations. Oraganoleptic evaluation of developed cookies was carried out by a panel of 5 semi trained panel members and best product was selected based on the results from the score card. The sensory evaluations for three heat treatments were good in taste. The body and texture, consistency of fried cookies were reported to be too soft because of porous structure developed during frying process; heat is transferred from hot oil to the product surface by convection and from the surface to the centre   Values are means±standard deviation from five parallel observations Same letters within the same column do not differ significantly (p < 0.05) according to Tukey's test by conduction. The liquid water moves from inside of the fries to the evaporation zone leaving the product from the surface as vapour. Some of this vapour though, may remain trapped within the pores due to restrictive intercellular diffusion. The vapour in this confined space will expand and become superheated, distorting the pore walls and contributing to total porosity [13,14]. As the sweet potato flour concentration increased, the softness is decreased. It was reported in baking and microwave heat treatments were almost same but crust is for in baked cookies. One of the most important changes is the product evolving from semi-viscous dough to a solid alveolar structure at the end of baking. Air bubbles, introduced during the mixing of ingredients expand within the product during baking and contribute also to the volume expansion although to a lesser extent. Finally, upon baking the water evaporation/condensation within the product structure results in a significant moisture loss qualified as moderate drying.
Another important reaction influencing the quality of baked product is the appropriate brown color development on the surface by sugar caramelization, Maillard reactions, starch dextrination and/roasting of protein network [15]. Where as in micro wave heating process avoids the problem of crust formation and surface browning. In contrast to conventional baking microwave heating inactivates this enzyme fast enough (due to a fast and uniform temperature rise in the whole product) to prevent the starch from extensive breakdown, and develops sufficient CO2 and steam to produce a highly porous [16].
Crispness is more in 40% sweet potato flour incorporated cookies (T 3 HT 1, T 3 HT 2 ) as per the sensory evaluation. The overall acceptability of the cookies was almost similar in baking and microwave heat treatments.

Microbiological Assay of Different Types of Cookies
The obtained results for standard plate count (SPC), Yeast and mould and Coli forms in developed cookies are presented in Tables 3.2a, 3.2b and 3.2c. On 0 th day the SPC for baked cookies was more in T 5 HT 1 (3.600±0.894) which was recorded in 40% whey protein concentrate (WPC-80), incorporated cookies and least in T 2 HT 1 as the days increased standard plate count (SPC) gradually increased. Yeast and mould count was recorded nil in 0 th and 15 th where as on 30 th T 5 HT 1 was recorded as 0.200±0.00 where as in Coli forms was highest on 30 th day in T 1 HT 1 (2.800±0.447) and the least was recorded on 0 th day (Nil).
In microwave treated cookies SPC is high in T 1 HT 2 (2.200±0.837) and T 3

CONCLUSION
From the present study, it could concluded that the 20% SPF and 20% WPC (T 3 HT 1 and T 3 HT2)-supplemented cookie samples were nutritionally rich as well as more sensory acceptable product with regardless of both baking and microwave heat treatments. Evaluation results revealed that 40% SPF (T 1 HT 3 ) are also good in taste. The standard plate Count, yeast and mould count and coli forms of cookie samples were found within the acceptable limits. Thus, the present our study concludes that the supplementation level of 20% SPF and 20% WPC (T 3 HT 1 ) results are acceptable in the sensory, textural and nutritional characteristics.

ACKNOWLEDGEMENT
This paper is part of Ph.D research which has been conducted at SHAUTS, Authors are thankful for the university for providing necessary facilites to complete this research work.