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Shelf-Life Study of Fortified Peanut Butter
Production of Fortified Peanut Butter
One hundred (100) Kg of fortified peanut butter was prepared using a premix to plain peanut
butter weight ratio of 1:25. This was done by adding 2 Kg of pre-weighed premix in 50 Kg pre-weighed
plain peanut butter. The premix was manually mixed with the plain peanut butter with the aid of a plastic
spatula until a homogenous mixture was achieved. Above steps were repeated in another container of 50
Kg pre-weighed peanut butter. The mixtures in the two separate containers were transferred to a
horizontal mixer and allowed to mix for 10 min. After mixing, the fortified product was transferred to a
filling machine, and filled in glass tumblers with a capacity of 155 g. A plastic tape was wrapped around
the metal lids and glass tumbler for added protection together with a tamper proof plastic seal.
Shelf-Life Testing of Fortified Peanut Butter
The main objective of the study was to estimate the shelf-life of the vitamin A added in fortified
peanut butter based on 20% loss of vitamin A from the claimed value of 4.6 μg retinol/g peanut butter.
Other product characteristics likely to affect shelf life of the product such as presence of rancid-like odor
and oil separation were likewise evaluated. The shelf-life study was conducted using the accelerated
shelf-life method as follows: fortified peanut butter was packed in 155 g glass bottles and stored at three
accelerated temperatures, i.e. 35, 40 and 45 o C and at room condition (≈30 o C). Prior to storage of the
product at the above accelerated temperatures and at ambient condition, sampling was conducted at predetermined
storage times and evaluated for its physical, chemical and sensory characteristics.
Evaluation of the Product
The physical characteristics of the product were evaluated as to the condition of the glass tumbler
and caps (which were checked visually for presence of defects such as oil leaks in the caps and sides of
the glass tumbler, dirt on the caps and cracks and breaks in the bottle), and appearance of the product (oil
separation in particular which was measured using a vernier caliper as soon as the bottle was opened).
The sensory characteristics of the product were evaluated by six trained panelists. Descriptive
testing was used to evaluate the initial quality of the product based on color, odor, flavor, and product
acceptability. For succeeding evaluations, only the presence of rancid-like odor was evaluated.
For the chemical characteristics of the fortified product, the level of vitamin A, expressed as
microgram retinol per gram (μg/g) peanut butter and the peroxide value, expressed as milligram
peroxide/Kg of oil were evaluated. At pre-determined storage times, two replicate samples were analyzed
for vitamin A content for each storage temperatures. For peroxide value analysis, samples were taken
only at the start, 3 rd month and 6 th month of storage of the product at ambient temperature.
Estimation of Shelf-Life of Vitamin A
To estimate the shelf-life of vitamin A in the fortified product, the average vitamin A
concentration of the replicate samples was plotted against storage time for the given accelerated
temperatures. The lines were fitted to the points by linear regression using the Kwikstat 4 computer
statistical software. The rates of vitamin A loss were determined by calculating for the slope of the linear
regression equation between the amount of vitamin A and storage time. To determine the temperature
relationship of the rate of vitamin A loss of the fortified product, the Arrhenius relationship (Labuza,
1984) was used. This was done by plotting the natural logarithm (ln) of the rate of vitamin A loss at the
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