Department of Food Science & Technology
Adding Value to Agricultural Waist Products:
Utilizing Peanut Hulls for
Consumer Acceptable Baking Applications
By Maretta Day Zonio Jankowski
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Area Harvested1 |
Yield2 |
Production3 |
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1996 |
1997 |
1998* |
1996 |
1997 |
1998* |
1996 |
1997 |
1998* |
|
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Acres |
Pounds |
1,000 Pounds |
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|
|
191.0 |
193.0 |
196.0 |
2,355 |
1,930 |
2,000 |
449,805 |
372,490 |
392,000 |
|
|
82.0 |
84.0 |
81.0 |
2,880 |
2,715 |
2,200 |
236,160 |
228,060 |
178,200 |
|
|
533.0 |
519.0 |
533.0 |
2,690 |
2,570 |
2,500 |
1,433,770 |
1,333,830 |
1,332,500 |
|
|
16.5 |
17.3 |
20.0 |
2,300 |
2,700 |
2,500 |
37,950 |
46,710 |
50,000 |
|
|
125.0 |
121.0 |
125.0 |
2,940 |
2,720 |
3,000 |
367,500 |
329,120 |
375,000 |
|
|
81.0 |
77.0 |
75.0 |
2,410 |
2,400 |
2,200 |
195,210 |
184,800 |
165,000 |
|
|
10.5 |
10.5 |
10.5 |
3,100 |
2,900 |
1,900 |
32,550 |
30,450 |
19,950 |
|
|
265.0 |
315.0 |
360.0 |
2,600 |
2,610 |
2,500 |
689,000 |
822,150 |
900,000 |
|
|
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
Peanut butter accounts for approximately half of the
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
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
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.
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 |
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Components, % |
Peanut |
|
Moisture |
7.92 ± 0.23 |
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Crude Protein |
6.90 ± 0.22 |
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Ether Extract (Fat Analysis) |
1.30 ± 0.19 |
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Ash Content |
4.23 ± 0.08 |
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Crude Fiber |
49.2 ± 0.35 |
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Source: Die Nahrung 35 (1991) |
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What
has been made with Peanut
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
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.
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Sample Formula for peanut
cookies using peanut hull flour |
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Ingredients |
Amount |
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Egg |
5% |
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Brown Sugar |
20% |
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Wheat flour (all propose) |
31% |
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Peanut |
4% |
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Baking soda |
1.9% |
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Salt |
.6% |
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Vegetable Oil |
10% |
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Vanilla Extract |
2.5% |
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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,
Collins, JL, Kalantari SM,
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
http://www.branluebbe.com/sites/wcb/products/disperse/colloid.htm
George Washington Carver
National Monument Website:
http://www.nps.gov/gwca/expanded/peanut.htm