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Department of Food Science & Technology

 

 

Adding Value to Agricultural Waist Products:

Utilizing Peanut Hulls for Consumer Acceptable Baking Applications

By Maretta Day Zonio Jankowski

 

Georgia & Our Peanuts

 

Georgia being the number one producer of peanuts in the United States, accounting for 41% of US peanuts, the state boasts a large agricultural connection to the peanut industry. Peanuts are the 12th most valuable cash crop grown in the United States with a farm value of over one billion U.S. dollars.

 

U.S. Peanut Production by State

 

 

 

Area Harvested1

Yield2

Production3

1996

1997

1998*

1996

1997

1998*

1996

1997

1998*

Acres

Pounds

1,000 Pounds

ALABAMA

191.0

193.0

196.0

2,355

1,930

2,000

449,805

372,490

392,000

FLORIDA

82.0

84.0

81.0

2,880

2,715

2,200

236,160

228,060

178,200

GEORGIA

533.0

519.0

533.0

2,690

2,570

2,500

1,433,770

1,333,830

1,332,500

NEW MEXICO

16.5

17.3

20.0

2,300

2,700

2,500

37,950

46,710

50,000

NORTH CAROLINA

125.0

121.0

125.0

2,940

2,720

3,000

367,500

329,120

375,000

OKLAHOMA

81.0

77.0

75.0

2,410

2,400

2,200

195,210

184,800

165,000

SOUTH CAROLINA

10.5

10.5

10.5

3,100

2,900

1,900

32,550

30,450

19,950

TEXAS

265.0

315.0

360.0

2,600

2,610

2,500

689,000

822,150

900,000

VIRGINIA

76.0

74.0

75.0

2,885

2,560

2,650

219,260

189,440

198,750

UNITED STATES

1,380.0

1,410.8

1,475.5

2,653

2,507

2,459

3,661,205

3,537,050

3,611,400

*Estimated
1Thousands of acres
2Pounds per acre
3Production comprised of quota and non-quota peanuts in thousands of pounds
Source: USDA, NASS

Most of the U.S. peanut crop is used in domestic edible products each year. Peanuts, peanut butter and peanut candy are some of the most popular products in the United States. American consumers eat more than 6 pounds or 2.7 kilograms of peanut products each year, worth more than $2 billion at the retail level.

Peanut butter accounts for approximately half of the U.S. edible use of peanuts, accounting for $850 million in retail sales annually. The other half of U.S. edible consumption is divided equally between snack nuts and confectionery.

 

What about the Hulls?

 

In order to get all those peanuts to become peanut butter manufactures need to go thru the process of shelling the nuts. In the first step of the shelling process, peanuts are cleaned; removing stones, soil, bits of vines and other foreign materials that are commonly harvested along with the nuts. The cleaned peanuts move by conveyor to shelling machines where peanuts are de-hulled as they are forced through perforated grates. The peanuts then pass through updraft air columns that separate the kernels from the hulls. Specific gravity machines separate the kernels and the unshelled pods. The kernels are then passed over the various perforated grading screens where they are sorted by size into market grades. But what about the hulls?

 

Model 205 PEARMAN Peanut Moisture Sample Sheller.

Source: Pearman Corporation

 

Because the prime market for U.S. peanuts is in edible consumption, and the marketing and production focus is in that direction; it can be said that the use of peanuts and peanut products are a valuable commodity. The major waist product from the processing of peanuts is its hull. Finding practical applications for this waist product can have a great impact on the economy of the peanut industry. Converting a low value or waste material in high value product in the United States peanut industry is not a new idea, it is probably as old as the peanut itself, which it is said that the peanut made its way to North America on sailing ships in the 1700’s. As a matter of fact Dr. George Washington Carver, a noteworthy African-American Scientist, is famed for the creation of over 300 products made from peanuts, including peanut hull bran, meal & flour.

Utilizing peanut hulls wouldn’t be too difficult; they are an excellent source of cellulose and crude fiber. Incorporating higher amounts of fiber into the diet to supplement food products by use of addition of fibrous materials can benefit consumers that are interested in a wide range of health benefits. Foods that contain significant amounts of fiber are generally lower in caloric content than similar foods with little or no fiber. This lowered caloric consumption can aid in weight reduction for consumers. The advantages of increasing fiber intake do go beyond weight loss aspirations; dietary fiber intake can reduce the several disorders including diverticular disease, colon cancer, constipation, ischemic heart disease, diabetes and numerous other gastrointestinal disorders.  On a chemical level, the principal advantages of peanut hulls are their high liquidity absorbency, chemical inertness and biodegradability.

Making Peanut Hull Flour

To date there have been many non-food applications of peanut hulls ranging from plastic composite materials to pesticide and fertilizer carriers, and peanut hulls are of great use as industrial absorbents. But uses in food applications have so far been limited. A useful application of peanut hulls in food products would be to mill the hulls down into flour

 

In order to make flour from peanut hulls they must first be separated form the debris by screening, this has been done with success by use of hardware cloth with 6.3 mm square openings. The screened material then should be washed in a solution of dodecyl sulfate, and rinsed with up to 3 changes of fresh water. Then the hulls must be dried, a forced-air dehydrator at 85˚C for 24 hours will do the trick. Toasting the hulls prior to milling at 149˚C for 1 hour is an optional step.

 

Waukesha Cherry-Burrell

Colloid Mill

 

 

Now the hulls are prepared for milling, grinding the hulls may take up to 3 times thru the mill in order for them to pass a 40-mesh sieve; this is followed by pulverizing the material in a colloid mill until it becomes possible to pass thru an 80-mesh sieve. Thus, created is the peanut hull flour containing 49.2% crude fiber and little protein and fat.

 

Proximate Analysis

of peanut hull flour on dry basis

Components, %

Peanut Hull Flour

Moisture

7.92 ± 0.23

Crude Protein

6.90 ± 0.22

Ether Extract (Fat Analysis)

1.30 ± 0.19

Ash Content

4.23 ± 0.08

Crude Fiber

49.2 ± 0.35

Source: Die Nahrung 35 (1991)

 

 

What has been made with Peanut Hull Flour?

 

Previous studies have shown some success with peanut hull flour being used in wheat bread and in low-calorie cakes, but non of these processes have been adapted for industrial or commercial use. From these studies peanut hull flour is said to impart a slight almost negligible amount of peanut flavor to the final product.

 

Collins study of wheat bread made with peanut hull flour explored the use of peanut hull flour as a source of dietary fiber. It was found that using a formulation that contained 4% peanut hull flour produced bread that should be consumer acceptable. The attributes of this 4% peanut hull flour bread faired better than the bread produced with 8% peanut hull flour in the sensory panels where surface smoothness, moistness, graininess, grittiness, hardness of crust, chewiness, stickiness, and hardness of crumb were rated. The bread was also tested for textural properties, proximate composition, dietary fiber content, specific volume, and color. Gritty sensation was detected with the peanut hull flour breads but to a small degree.

 

Low-calorie cakes made with peanut hull flour were tested for their differing levels of peanut hull flour and the effect on its physical attributes as well as a sensory evaluation. This study by Hegazy revealed that the flavor and general acceptance of cakes prepared with 30% peanut hull flour was significantly less accepted compared to those prepared with 10 and 20%. Testing included water holding and oil holding capacity, Aflatoxin detection, and proximate composition. Sensory evaluation of the characteristics: color, texture, tenderness, moistness, and flavor were also conducted.

 

It was found that increasing levels of peanut hull flour in these baked products contributed to darker color, harder crust, no difference in chewiness, decrease in stickiness, and increase in crumb softness. But overall the lower levels of peanut hull flour in the products were found most consumer acceptable.

 

What can be made with Peanut Hull Flour?

 

Many baking applications can come from the use of peanut hull flour such as cookies, crackers or even baked chips. The first step is to create a formula for the product; this may be done by modifying an existing formula by replacing a small percentage of the wheat flour for the peanut hull flour. The following is an example of a formula for peanut cookies that has an inclusion of peanut hull flour.

 

Sample Formula for peanut cookies

using peanut hull flour

Ingredients

Amount

Egg

5%

Brown Sugar

20%

Wheat flour (all propose)

31%

Peanut Hull Flour

4%

Baking soda

1.9%

Salt

.6%

Vegetable Oil

10%

Vanilla Extract

2.5%

Chopped Roasted Peanuts

25%

 

When formulating a product that has peanut hull flour as a supplement one must consider that success in the previous experiments was examined with lower levels of peanut hull flour. Also due to the nature of peanut hull flours high absorbency it may be necessary to adjust liquids content, but this is dependant on the type baked product that is being formulated. For example, cookies would have a higher moisture content that that of a cracker or baked chip.

 

Other sensory characteristics should also be considered such as color, flavor and texture. Toasting the hulls prior to milling at 149˚C for 1 hour would provide a slightly darker color and in combination with solvent extraction can diminish any bitter flavor that the material may impart to the baked product. The aforementioned studies on the wheat bread and in low-calorie cakes with peanut hull flour have stated that peanut hull flour imparts a slight or weak peanut flavor to the final product.  The formula above was chosen because the acceptability of baked products may increase if the products are featuring peanut flavors. Milling the flour thru a 100-mesh sieve will decrease the particle size of the flour giving it a lighter, less gritty texture.

 

After finding a formulation a procedure must be developed, this too can be done by using an existing procedure, and thru baking test can be modified. With the previous baking applications that have been examined there was no adjustment in baking procedure necessary.

 

So how is it?

 

            After achieving the final baked product it is time to test it. Before any sensory evaluation of the product it is beneficial to do any analytical test on the product first, not only does this insure that you will have product available to do this testing but also you can determine if the product fits within the specified goal. For example a limit is set in hypothesis to how much dietary fiber that is to be obtained from the product, and the product does not meet those expectations, then it would not be beneficial to conduct a sensory evaluation no the product. On the other hand, you may not meet this parameter set in the hypothesis if consumer acceptability is the key goal of the product. With supplementation these goals should be balanced, the objective is to create a product that imparts more dietary fiber in the diet and at the same time will be something that the consumer will want to eat.

 

To determine consumer acceptability sensory evaluation should be conducted. The most effective method would be to use a blind taste panel. With this evaluation panelist can help you determine if they detect a difference, and score their preference. Difference testing using triangle testing provides information about if the peanut hull flour is detectable or not. This is done in comparison with a control, or sample of product without the peanut hull flour substitution. Preference testing would provide information about how the product stands in the taste of the consumer. A 9-point hedonic scale can be used for overall preference evaluation, and an interval scale for evaluation for individual characteristics.

 

Example of 9-point hedonic scale

 

Sample ______

Indicate your feelings on the sample by marking one of the following choices

9

LIKE EXTREMELY

8

LIKE VERY MUCH

7

LIKE MODERATELY

6

LIKE SLIGHTLY

5

NEITHER LIKE NOR DISLIKE

4

DISLIKE SLIGHTLY

3

DISLIKE MODERATELY

2

DISLIKE VERY MUCH

1

DISLIKE EXTREMELY

 

Example of an interval scale

 

The following lines represent a scale from 0 to 150, with one mark at 12.5 and the other at 137.5.  Please write down the sample number/name and the sensory characteristic you are quantifying above the line.  An example is provided for you.

      Sweetness      

_________________________x______________________________________________

                                            ~40                                                                                    

References

Article References

Collins, JL, Post AR (1981) Peanut hull flour as a potential source of dietary fiber. J Food Sci 46: 445-448,451.

 

Collins, JL, Kalantari SM, Post AR (1982) Peanut hull flour as a dietary fiber in wheat bread. J Food Sci 47: 1899-1902, 1920.

 

McKee LH, Latner TA (2000) Underutilized sources of dietary fiber: A review. Plant Foods for Human Nutrition (Formerly Qualitas Plantarum) 55: 285-304.

 

Hegazy NA, Mekawy AA, Hassona HZ (1991) Influence of different levels of peanut hull flour on physical and sensory evaluation of low calorie cakes. Die Nahrung 35(8):821-826.

 

Internet References

The American Peanut Council website:

http://www.peanutsusa.com/index.cfm?fuseaction=home.page&pid=12

 

Pearman Corporation Agricultural Equipment Website:
http://www.pearmancorp.com

 

Waukesha Cherry-Burrell Processing Equipment Website:

http://www.branluebbe.com/sites/wcb/products/disperse/colloid.htm

 

 

George Washington Carver National Monument Website:

http://www.nps.gov/gwca/expanded/peanut.htm