Quality Characteristics Of Biscuit Produced With Wheat-Sweet Potatoes Composite Flour

Project and Seminar Material for Food Science and Technology (FST)

Quality Characteristics Of Biscuit Produced With Wheat-Sweet Potatoes Composite Flour


Chapter One


1.0 Introduction

Sweet potato (Ipomoea batatas) is an extremely versatile and delicious vegetable that possesses high nutritional value (Mohanraj and Sivasankar 2014). Among the world’s major food crops, sweet potato produces the highest amount of edible energy per hectare per day (Sukhcharn et al. 2008). Sweet potato consists of about 70% carbohydrates (dry basis) of which a major portion is starch, which can be utilized as a functional ingredient in certain food preparations (Avula 2005). It is an excellent source of vitamin A (in the form of beta – carotene) and also a very good source of vitamin C and Manganese. In addition, sweet potatoes are a good source of dietary fiber, natural sugars, protein, niacin, vitamin B5, vitamin B6, vitamin E, potassium, biotin, iron, calcium and copper (“The world healthiest foods”, 2017).

Sweet potato is commonly referred to as a subsistence, food security or famine relief crop. Its uses have diversified considerably in the developing countries. Sri Lanka has a long history of cultivation of sweet potatoes. It is considered as a crop of exotic origin, but people regard it as indigenous because it has been in cultivation in Sri Lanka as an important traditional food crop since ancient times (Karunathilake 2005). Options for sweet potato products are numerous, and based on recent diagnostic assessments carried out in developing countries, dried chips, starch and flour have been identified as among the most promising products (Collins 1989).

The raw material of foremost importance in bakery product is the wheat flour. Wheat is the main raw material for bakery, biscuit and paste (Diana et al. 2007). Bakery products are commonly made from wheat flour containing gluten, whereas gluten contributes to the typical texture, flavour and form of the usual bread and cake products. Without gluten, baked goods will not hold their shape. That is why wheat flour is used in baking. There is however circumstances in which wheat flour are not readily available, or if people in these areas nevertheless wish to change to the consumption of the bread so that they will need to import wheat and pay for it.

A mixture of wheat flour and sweet potato flour could make a good baking product, which should increase its economic value (Zuraida 2003). Most of the technical research on sweet potato flour focused on the development of new products using sweet potato flour rather than on efficient methods to produce and store the flour (Lizado and Guzman, 1982; Sukhcharn et al. 2008). Addition of various proportion of sweet potato flour in wheat flour can increase the nutritive values in terms of fiber and carotenoids and also helps in lowering the gluten level and prevent humans from coeliac disease (Tilman et al. 2003).

Sri Lanka has a long history of sweet potato cultivation. Extent and production of sweet potato are 3,270 hectares and 25,780 metric tons in 2010 (Department of Census and Statistics of Sri Lanka, 2010). Sweet potato can be grown successfully throughout the year in all agro-ecological zones. In Sri Lanka, they are cultivated in all the districts but mainly in Ratnapura, Hambantota, Kurunagale, Gampaha, Kagalle, Badulla and Kalutura districts. In dry zone the cultivation area of sweet potato is low compared to wet zone and intermediate zone (Department of Census and Statistics of Sri Lanka, 2010). It is considered as a crop of exotic origin, but people regard it as indigenous because it has been in cultivation in Sri Lanka as an important traditional food crop from very ancient time (Karunathilake 2005).

Sweet potato based products are of high quality and could compete with the existing products in the market (Sneha et al. 2012). The use of sweet potato flour for supplementing with wheat flour in the bakery industry could substantially reduce the need for wheat being imported, reduce the usage of sugar on the products and increase the value of sweet potato. The objective of present study is to replace the wheat flour in cookies with sweet potato flour (gluten – free flours) in order to increase the fiber and other nutrients and develop cookies resembles as closely as possible to the wheat flour based product.


1.2 Sweet Potato Nutrition Facts

Sweet potatoes are high in many important nutrients. They contain a good amount of fiber as well as vitamin A, vitamin C, manganese and several other vitamins and minerals.
One medium cooked sweet potato contains approximately:

  1. 103 calories
  2. 23.6 grams carbohydrates
  3. 2.3 grams protein
  4. 0.2 gram fat
  5. 3.8 grams dietary fiber
  6. 21,907 international units vitamin A (438 percent DV)
  7. 22.3 miligrams vitamin C (37 percent DV)
  8. 0.6 milligram manganese (28 percent DV)
  9. 0.3 milligram vitamin B6 (16 percent DV)
  10. 541 milligrams potassium (15 percent DV)
  11. 1 milligram pantothenic acid (10 percent DV)
  12. 0.2 milligram copper (9 percent DV)
  13. 1.7 milligrams niacin (8 percent DV)
  14. 0.1 milligram thiamine (8 percent DV)
  15. 30.8 milligrams magnesium (8 percent DV)

In addition to the nutrients above, sweet potato nutrition also contains riboflavin, phosphorus, vitamin E, vitamin K, calcium and iron.


1.3 Sweet Potato Nutrition: Sweet Potato Benefits

  1. Stabilizes Blood Sugar
  2. High in Antioxidants
  3. Boosts Brain Function
  4. Enhances Immunity
  5. Promotes Vision Health
  6. Aids in Weight Loss
1. Stabilizes Blood Sugar

Sweet potatoes are an excellent dietary addition for those with diabetes as they have been shown to help reduce and regulate blood sugar levels. In fact, there are several studies focused on learning more about the connection between the sweet potato and diabetes. Caiapo, in particular, is a type of white sweet potato that has been studied extensively for its anti-diabetic properties.

In one study out of the University of Vienna in Austria, 61 participants with diabetes were given either four grams of Caiapo or a placebo daily for three months. At the end of the study, the sweet potato group had significantly lower blood sugar levels than the control group.

Another small study published in the journal Metabolism showed that treating diabetic patients with Caiapo for six weeks helped improve insulin sensitivity. Insulin is the hormone responsible for the transport of sugar from the blood to the tissues where it can be used as energy. Improvements in insulin sensitivity allow it to work more efficiently in the body to maintain normal blood sugar.

Additionally, sweet potatoes are high in fiber, with each medium sweet potato fulfilling up to 15 percent of your fiber needs for the entire day. Fiber slows the absorption of sugar to help prevent spikes and crashes in blood sugar levels.

2. High in Antioxidants

Antioxidants are compounds that help fight off harmful free radicals to reduce the risk of chronic disease and prevent damage to the cells. Antioxidants may protect against diabetes, heart disease and even cancer. Besides being rich in fiber and many important vitamins and minerals, sweet potatoes are also loaded with these beneficial antioxidants.

Orange-fleshed sweet potatoes are especially high in beta-carotene, which is the pigment responsible for their characteristic vibrant orange flesh. Beta-carotene is a powerful antioxidant that can help promote healthy vision, improve respiratory health and even protect your skin.

Studies show that colored sweet potatoes, in general, exhibit more potent activity against free radicals than white sweet potatoes with purple potatoes, specifically, containing the highest amount of antioxidants.
In addition to sweet potatoes, other top antioxidant foods include goji berries, blueberries, dark chocolate and pecans.

3. Boosts Brain Function

Some research has found that eating sweet potatoes could help boost brain function and improve memory thanks to their abundance of nutrients and antioxidants.

One animal study out of Chungnam National University’s College of Pharmacy in Korea, for instance, treated rats with purple sweet potato extract and found that it prevented oxidative damage in the brain, enhanced cognitive performance and improved memory. (9)

Another animal study conducted in China in 2010 showed that purple sweet potato extract helped protect against brain aging and improved spatial learning and memory ability in mice.

Avocados, beets, broccoli and leafy green vegetables are examples of other brain foods that can help boost focus and memory.

4. Enhances Immunity

Sweet potato nutrition is jam-packed with vitamin A, with each medium potato cramming in about 438 percent of the daily vitamin A requirement. This vitamin plays a role in many aspects of health, but it is especially important in terms of immunity.

Vitamin A helps stimulate the production of immune cells that fight off disease and infection. It also can help kill off harmful cells and has been shown to have anti-tumor properties in some animal studies. Many studies have even reported that vitamin A supplementation can help reduce the risk of death from infectious diseases in certain areas where vitamin A deficiency is common.

Getting enough vitamin A from foods like sweet potatoes is crucial to maintaining healthy immune function. Other top vitamin A foods include carrots, kale, spinach and apricots.

5. Promotes Vision Health

In addition to boosting immunity, vitamin A is also integral to maintaining healthy vision. A deficiency of vitamin A can result in symptoms like dry eyes, night blindness, a buildup of keratin on the conjunctiva and even total vision loss in severe cases.

One medium sweet potato can meet and exceed your daily vitamin A needs. In fact, if you can squeeze even just one-fourth of a sweet potato into your diet, you’re set for the entire day.

Not only that, but sweet potatoes also contain important antioxidants that can contribute to vision health as well. Beta-carotene, for example, has been shown to slow the progression of age-related macular degeneration, a condition that can result in vision loss.

Other eye vitamins that you should incorporate into your diet include vitamin C, zinc and omega-3 fatty acids.

6. Aids in Weight Loss

If you have a few stubborn pounds that you’re trying to lose, incorporating this nutritious root vegetable into your diet may be able to help. The sweet potato benefits weight loss because it’s super nutrient-dense and loaded with fiber to help keep you full.

Fiber moves slowly through the digestive tract, helping promote satiety and cut cravings to aid in weight loss. Just one cup of sweet potatoes boasts a whopping 6.6 grams of fiber, or up to 26 percent of what you need for the entire day.

A recent 2017 animal study also found that purple sweet potatoes, in particular, may have extra weight-busting benefits. Mice were fed a high-fat diet and were supplemented with purple sweet potatoes, which were shown to reduce body weight and fat accumulation over a 12-week period.

Of course, sweet potatoes should be paired with a healthy diet and regular exercise to achieve maximum weight loss. Fortunately, not only do sweet potatoes aid in weight loss, but they can also help you achieve your fitness goals as well. Sweet potato benefits bodybuilding because it is slowly digested, providing you with long-lasting energy to fuel you through your gym session.


1.4 Objectives of Study

  1. To know the means of making biscuits from sweet potato flour
  2. To learn the characteristics of biscuits made from potato flour

Chapter Five


5.0 Discussion of Finding, Conclusion and Recommendations

5.1 Findings

The protein content as revealed by the results showed that protein ranges from 4.50g/100g to 8.92 g/100g. The result revealed that, biscuits produced from ratio 100:0 wheat-sweet potato flour has the highest protein content, with the amount of protein decreasing as the quantity of potato flour increases. This may be because of the fact that raw wheat contains more protein than raw potato. This result is in line with the work of Khaliduzzaman et al. (2010) which states that wheat flour contains more protein than potato flour. The concentration of fat in the biscuits ranged between 10.90g/100g and 18.93G/100G, with highest concentration of fat (18.93G/100g) seen in biscuits produced from ratio 100:0 wheat-potato flour. This result showed that fat concentration decreases as the quantity of potato flour increases, this result is in agreement with the work of Idowu et al. (1996) which stated that the nutritional qualities decreases as the level of starchy staples increases. However, biscuits with reasonable concentration of fat were produced from all ratios of wheat-sweet potato composite flour. The value of ash ranged between 2.22g/100g and 4.58G/100G, with the highest value (4.58G/100g) seen in biscuits produced from 90:10 ratio of wheat-potato flour, and lowest value of ash was recorded in biscuits made from ratio 60:40 wheat-potato composite flour. The ash content of food material could be used as an index of mineral constituents of the food because ash is the inorganic residue remaining after the water and organic matter have been removed by heating in the presence of an oxidizing agent (Sanni et al., 2008). The value of crude fiber (3.16g/100g to 5.10g/100g) increases as more potato flour is added to wheat flour in biscuit production. The highest value (5.10g/100g) of crude fiber was seen in biscuits produced from ratio 50:50 wheat-potato flour. These results suggest that potato flour has more crude fibre than wheat flour. Biscuits made from ratio 50:50 wheat-sweet potato flour recorded the highest value (12.71%) of moisture; the lowest moisture content (9.34%) was recorded in biscuit made from 100:0 ratio of wheat-sweet potato composite flour. There was increase in moisture as more potato flour is added to wheat flour; this result is in agreement with the work of (Khaliduzzaman et al., 2010) when he supplemented wheat flour with 20% potato flour in making biscuits. Carbohydrate value range between 56.52g/100g and 64.75g/100g; the highest value was recorded in 100:0 ratios of wheat-sweet potato biscuit.

Despite the fact that mineral content of raw wheat are higher than mineral content of raw sweet potato, it was observed from the results that the mineral value of calcium, magnesium, potassium, sodium and phosphorus are higher in biscuits made from ratio 90:10, 70:30, 60:40 and 50:50 wheat- sweet potato composite flour than biscuits made from ratio 100:0 of wheat-sweet potato composite flour. These results suggest that biscuit of good mineral content can be produced when wheat flour is substituted with sweet potato flour.

The bulk density is a reflection of the load the samples can carry if allowed to rest directly on one another. The results showed that flour mixture of ratio 100:0 wheat-sweet potato composite flour has higher value (0.9091g/cm3) of Bulk Density, while the lowest value (0.7407g/cm3) of bulk density was recorded in flour mixture of ratio 60:40 wheat-potato composite flour. The particle size and the density of flour or flour mixtures generally affect the bulk density and it is very important in determining the packaging requirement, raw material handling and application in wet processing in the food industry (Adebowale et al., 2008; Ajanaku et al., 2012). Flour of ratio 100:0 wheat-potato composite flour has the highest (2.41g/g) Water Absorption Capacity, and the mixed of ratio 60:40 has the lowest (1.88G/g) Water Absorption Capacity. Flour of ratio 100:0 wheat–sweet potato, has higher affinity for water, which is informed by its lower moisture content 9.34%. This could be indicative of the fact that wheat flour confers high water binding capacity than potato flour, which causes the reconstitution ability and textural properties of dough obtainable from wheat composite flour to be better than that of wheat-sweet potato flour composite. However, wheat-sweet potato flour composites display acceptable binding properties during preparation, which suggest that the combination of wheat-sweet potato composite can be use in making biscuit. The lose structure of starch polymers causes it to possess high water absorption capacity while products with low value indicates the compactness of such product structure.

One of the most important properties that influence quality and aesthetic considerations in the food industry is the pasting property, and they affect texture and digestibility as well as the end use of starch-based food commodities. Peak viscosity which ranged between 366.83RVU to 407.50 RVU is an index of the ability of starch-based fruits to swell freely before their physical break down (Sanni et al., 2006). The Trough value ranges from 236.33RVU to 291.08RVU, with biscuits made from ratio 90:10 wheat-sweet potato flour having the highest value and biscuits made from ratio of 50:50 wheat-sweet potato flour having the lowest value. Trough is the minimum viscosity value in the constant temperature phase of the RVA pasting profile and it measures the ability of the paste to withstand break down during cooling (Adebowale et al., 2012). The highest Break Down Viscosity (89.08 RVU) was recorded on biscuit produced from ratio 50:50 wheat-sweet potato composite flour, while biscuits produced from ratio 100:0 wheat-sweet potato composite flour has the lowest breakdown viscosity (54.67 RVU). The Final Viscosity ranged between 286.92RVU and 329.25 RVU with biscuit of ratio 90:10 wheat-sweet potato composite flour having the highest value and biscuits of ratio 50:50 wheat-sweet potato flour having the lowest value (329.25RVU). Final viscosity is commonly used to define the quality of particular starch-based flour, since it indicates the ability of the flour to form a viscous paste after cooking and cooling (Adebowale et al., 2012). The setback value ranged between 70.33RVU to 107.58RVU.

There was an increase in setback value as the percentage of sweet potato flour increases in the biscuit. The higher the setback viscosity the lower the retro-gradation of the flour paste during cooling and the lower the staling rate of the product made from the flour (Adeyemi and Idowu, 1990). The Peak time is a measure of the cooking time, and it ranged between 7.50min and 8.93 min, with biscuits produced from ratio 90:10 wheat-sweet potato composite flour having the highest value and biscuits made from ratio 100:0 wheat-sweet potato flour having the lowest value of 7.50min. Pasting temperature ranged from 68.35OC to 91.40°C, and the highest pasting temperature was recorded in biscuits made from ratio 90:10 wheat-sweet potato composite flour. Adebowale et al., 2008 stated that a higher pasting temperature is an indication of higher water binding capacity, higher gelatinization tendency and lower swelling property of starch-based flour as a result of high degree of association between starch granules.

The results of Sensory evaluations reveal that biscuits produced from ratio 100:0 wheat- sweet potato composite are not significantly different (p≥0.05) in taste from biscuits made from ratio 90:10 and 70:30 wheat-sweet potato composite flour, but there was significant difference (p≤0.05) in taste between biscuits made from ratio 100:0 and biscuits produced from ratio 60:40 and 50:50 wheat-sweet potato composite flour. The results of the evaluation also reveal that there were no significant (p≥0.05) difference in colour and overall acceptability between biscuits produced from ratio 100:0 wheat-potato composite flour and biscuit made from ratio 90:10, 70:30, 60:40 and 50:50 wheat-potato composite. During evaluation, most of the panelist shown that biscuits made from ratio 100:0 and 90:10 are more acceptable, when they where ask to comment freely on the products, however, no significant differences was seen when the results were analyzed statistically.

Chinma et al. (2012) got a similar result in his sensory evaluation when he used unripe plantain to supplement wheat flour in the production of cookies; these results suggested that wheat flour could be supplement with other staple food samples in the production of biscuits and other baked food.


5.2 Conclusion

This research work was carried out in order to test for the nutritional, functional and sensory qualities of wheat-potato composite biscuits. The use of potato in supplementing wheat flour in biscuit production has significant benefits in countries where inadequate wheat is grown. Therefore, incorporation of sweet potato flour in biscuit production will reduce the quantity of wheat that will be imported, thereby reducing the cost of production of biscuits. Supplementing wheat with sweet potato flour in biscuits production will reduce over reliance on the use of wheat flour in biscuits production and other baked products, and it will enhance the utilization of sweet potato in the Nigeria. If wheat importation is reduced, and attention is given to potato farming, it will help strengthen the economy of the nation and provide income to farmers. A substantial amount of potato is spoiled and wasted due to inadequate cold storage facilities and insufficient post-harvest handling facilities in many developing countries. The experiments produced biscuits of acceptable Nutritional, Functional and Sensory qualities from all ratios of wheat-potato flour that was used; therefore, these research findings have unveil new windows for further utilization of sweet potato.


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