1

CHAPTER I

INTRODUCTION

1.1 Experimental Background

Shelf life can be defined as the time remained until the food is considered

not safe and no longer acceptable by the consumer. Usually, manufacturer

predicts the storage life of a food product under a given set of storage conditions

and each type of foods has different shelf life because they have different

characteristic.

There are two factors that can influence the shelf life of a food product

which are intrinsic and extrinsic factor. Intrinsic factors include water activity,

pH, redox potential, oxygen availability, nutrients, natural microflora, natural

biochemistry of the product and preservatives in a product while extrinsic factors

include time and temperature during processing, storage and distribution, relative

humidity, light expossure, composition of atmosphere, heat treatment and

consumer handling. Both intrisic and extrisic factors can inhibit or increases

several processes in food which can reduce the shelf life of the product itself

(Kilcast and Subramaniam, 2000).

Accelerated Shelf Life Testing method can be used in determining the

shelf life of food product, there are several principles that can be used to approach

ASLT, the most common one used is Arrhenius principle. Arrhenius stated an

equation which is a valid kinetic model for the rate of deterioration that happened

at different temperatures and constant moisture. Arrhenius implies that

deterioration of food is increasing when the food is kept in high temperature and

the equation can be used to determine the shelf life of a product (Kilcast and

Subramaniam, 2000).

1.2 Objective

The objective of this experiment is to learn the method to determine shelf

life of a food product (fruit juice and biscuit) by using one of Accelerated Shelf

Life Testing method which is Arrhenius method. This experiment also conducted

to study and undertand more about the application of Arrhenius method.

2

CHAPTER II

LITERATURE REVIEW

2.1 Factors Affecting Shelf Life

There are three factors affecting the shelf life of a product. First is the

microbiological changes, second is the moisture and water vapour transfer and the

third is the chemical and biochemical changes.

The rate of growth of spoilage microorganisms really determined the shelf

life of a food product, unless if the food has undergone a commercial sterilization

process or if the food product has water activity in which microbial growth will

not be permitted. The rate of growth of spoilage microorganism is determined by

several factors, such as the food properties (pH, total acidity, water activity,

presence of natural or added preservatives); environmental factors, like

temperature, relative humidity and gaseous atmosphere; any process which kills

or retard the growth of microorganisms, like thermal processing, freezing or

packaging; the type of microflora present in the food and its initial population

(Walker, 2009).

Moisture and water vapour transfer means the loss or gain of water

undergone by the food materials and this could affect much to the quality and also

the shelf life of the product. One way of dealing with this is by choosing the

proper packaging for the food product (Walker, 2009).

The most important chemical or biochemical changes are oxidation, non-

enzymic browning, enzymic browning and food-packaging interaction (in some

cases). Oxidation of fats and oils in food lead to the development of shorther-

chain fatty acids which caused the foul smell or rancid. Atmospheric oxygen are

not mainly the cause of fat oxidation; for example in frozen foods, the chemical

reactions could still happen in a much slower rate although the microbial activity

is arrested. Not only fats that are prone to oxidation, vitamins like ascorbic acid

and thiamine are very sensitive to oxygen. when vitamins are added to fortified

3

foods, vitamin degradation must be taken into account for the shelf life

determination (Walker, 2009).

2.2 Accelerated Shelf Life Testing

Accelerated Shelf Life Testing (ASLT) is a method used to evaluate

product stability in shorter period of time than the actual shelf life of product that

has valid kinetic model based on deterioration process that can be chemical,

physical, biochemical and microbial, with mostly ASLT studies done on chemical

deterioration of food. (Kilcast and Subramaniam, 2000). ASLT principle is done

by changing storage condition based on several factors that can increase

deterioration rate of food such as temperature, gas atmosphere and light. For

example, Arrhenius model is based on principle that increase of temperature can

increase deterioration process by raising rate of chemical reaction (Brody and

Lord, 2000). The test results then plotted in graph to predict relationship of shelf

life with normal storage condition, assuming that deteriorative process limiting

shelf life remains the same under the two conditions. There aIre two kinds of

approaches of ASLT such as initial rate approach and kinetic model approach

(Kilcast and Subramaniam, 2000).

2.3.1 Initial Rate Approach

According to Kilcast and Subramaniam (2000), initial rate approach is

considered as one of the simplest techniques for accelerating the shelf life testing.

Its application is done to cases where deteriorative process can be monitored by

extremely accurate and sensitive analytical method that is capable in measuring

changes for every minutes in extent of deterioration. Through this approach also,

kinetic data of initial rate of deterioration can be obtained even at very early stage

of the process. The actual shelf life can be predicted by knowing or evaluating the

behavior of detrioration process as function of time, provided by the term of order

of reaction (n) of chemical reaction. In the case of monitoring the change in

concentration of C of a component of interest, the kinetic equation may be

expressed as:

€

dCdt

with K as the kinetic constant and t is time. The index of deterioration (D)

formulated:

4

dD =

€

dCCn = K dt

The index of deterioration will be always linear with time and formulated as:

D - D0 = Kt

D0 is the initial level of the index of deterioration. It is the only kinetic model

required for employing initial rate approach of ASLT and extrapolation process,

after evaluating K from initial rate, product shelf life (ts) can be calculated as:

ts =

€

D−DoK

Most of the chemical deterioration reactions in foods can follow zero or first order

kinetic reaction. If the order of reaction is unknown, a simple accelerated test

procedure can be used to evaluate it empirically. In that case, the simplest version

of the kinetic model approach may be used. It uses any convenient kinetically

active factor to accelerate the deterioration process (Kilcast and Subramaniam,

2000).

The advantages of initial rate approach are ability to obtain kinetic data in

relatively short period of time at the actual storage conditions that requires only

the simplest kinetic model which relates solely to reaction order. In the absence of

a very sensitive and accurate analytical technique, the deterioration process should

be allowed to progress for longer time to enable available method for detecting

significant changes. Minimum time required for testing depends on the accuracy

and sensitivity of the analytical method. Therefore, the worse the method, the

longer time needed. To prevent this condition, proper analytical techniques

shouled be selected properly for monitoring the deterioration process is of great

importance to shorten the period of ASLT (Kilcast and Subramaniam, 2000).

2.3.2 Kinetic Model Approach

Kilcast and Subramaniam (2000) stated that kinetic model approach is the

most common method for ASLT. Basic principles of this approach are (1)

Selection of the desired kinetically active factors for acceleration of the

deterioration process. (2) Running a kinetic study of the deterioration process at

such levels of the accelerating factors that the rate of the deterioration is fast

enough. (3) Evaluation of kinetic model parameters done by extrapolating the data

5

to normal storage conditions. (4) Extrapolated data or the kinetic model resulted is

used to predict shelf life at actual storage conditions.

Valid kinetic model for the deterioration process is absolutely needed in

following procedural steps. The general and most comprehensive kinetic model

for chemical reactions in foods includes all the factors that may affect their rate,

can be divided into two main groups, which are compositional (CFi) and

environmental factors (EFj). The model can be generally expressed as:

€

dDdt

= K (CFi, EFj)

Kinetic constant (K) is a function of these factors (CFi, EFj). In predicting shelf

life of normal storage condition, the model should include only those factors that

change during storage (SFi), with required model formulated as:

€

dDdt

= K (SFi)

SFi are factors such as temperature, moisture content, light, composition, and

others that changes during storage. In predicting shelf life of a product at constant

temperature, no need to use kinetic model that includes this factor. Temperature

can be used very effectively to accelerate the rate of deterioration process.

Therefore, the demands from a kinetic model for ASLT can be different from one

that is used only to predict shelf life. The model for ASLT should contain two

groups of factors. The first includes factors which are changing during storage

(SFi) and the second includes factors used for accelerating the reaction rate (AFj).

Hence, the kinetic model for ASLT has the form:

€

dDdt

= K (SFi, AFj)

2.3.3 Problems in ASLT

According to Kilcast and Subaramaniam (2000), problems in ASLT can be

classified into three groups. First are the cases without valid kinetic model

believed to exist for any accelerating kinetic factor which eventually cause no

accelerated test procedure can be available for such a case. Second is when a

model does exist but it is very complicated and requires the evaluation of too

large number of parameters, thus causing experimental procedure can not be

practical in this case. Third are problems related to the application of valid ASLT

6

methods that includes the absence of deterioration index, time-dependent effects,

and statistical problems.

2.3 Arrhenius Model

Arrhenius model stated that the rate constant is exponentially related with

the reciprocal of absolute temperature. Arrhenius model is usually used to

determine the shelf life of food product. It related with the rate of a chemical

reaction to a changes in temperature (Kilcast and Subramaniam, 2000). The

equation is:

Where Ko is constant, Ea is energy of activation, R is the gas constant and

T is absolute temperature (in Kelvin). This Arrhenius model is widely used in

many cases, some using a ratio between the rates of reaction when the temperature

is changed by any arbitrary value to simplify the process and 10oC is the value

commonly used (Kilcast and Subramaniam, 2000). Thus, Q10 become the ratio

between the rate of reactions, Q10 equation also can be used to measure the

sensitivity of food product towards temperature, the equation is:

The equation using Q10 is commonly used to estimate the shelf life of a

food product. The rate of loss is inversely propotional to the shelf life which

means that when the rate of loss is increasing, the shelf life of a product is

decreasing and vice versa (Kilcast and Subramaniam, 2000).

7

Figure 2.x Arrhenius plot Source: Schmidl and Labuza (2000)

Straight line will be produced when a plot of the rate constant on semilog

paper as a function of reciprocal absolute temperature is made. When the reaction

is more temperature dependent, the graph will produce steeper slope which means

that when the temperature is increased, the reaction also increased or faster. In

order to plot the graph, there are several things needed which are: measurement of

loss of quality, endpoint value where the food is unacceptable for consumer,

measurement of time to reach the endpoint and at least two temperatures of

measurement of loss in a product. However, better statistical significance of a data

will be achieved if more temperatures are used (Office of Technology

Assessment, 1979).

2.4 Fruit Juice

Vitamin C is the most imporant paramater to determine the shelf life of

fruit juice especially for orange juice. Loss of vitamin C can happened due to heat

treatment, especially when it is heated with temperature above 60oC. Cullen et al

(2012) stated that the significant degradation of vitamin C is observed in isobaric-

isothermal treatment of orange juice at 850 Mpa, 65-80oC for 400 minutes and the

degradation follows first order kinetics. However, the ascorbic acid in tomato

juice is more stable than ascorbic acid in orange juice. The effect of treatment

depends on food composition and processing parameters such as pressure, time

and temperature. Other factors that influence the degradation of vitamin C are the

type of food matrix, oxygen availability and length of storage after treatments. For

the oxygen availability, less vitamin loss happened when there’s absence of

8

oxygen while high vitamin loss happened when the fruit juice is exposed to air. It

is happened because vitamin C is very sensitive to degradation caused by oxygen.

Oxygen can lead to oxidation and resulted in low vitamin C content presence in a

fruit juice. Ascorbic acid can be preserved if it’s treated with mild temperatures.

High pressure and short treatment time also has been proved to be better at

achieving more retention of vitamin C than low pressure and longer treatment

time (Zhang et al., 2011).

2.5 Biscuit

There are two types of biscuit which are dry biscuit and biscuit with

caramel, jam, or fruit paste. Dry biscuit has lower moisture content than biscuit

with caramel, jam, or fruit paste; thus, dry biscuit is more stable. The higher the

moisture content in biscuit will increase the rate of deterioration of the biscuit.

Type of biscuit deterioration is changes in physical and chemical characteristics

(Manley, 2000).

Changes in physical characteristics in biscuit include loss of crispness, fat

migration, changes in color, and flavor migration. Loss of crispness in biscuit

happened because of the moisture uptake since biscuit is hygroscopic. Fat

migration in biscuit can happened if there is inconsistent temperature during

storage. This condition can result in the development of fat bloom, crystallization

on the surface of the biscuits, and result in changes of surface color. Flavor

migration usually happens in biscuit that are packed as assortment where all of the

flavor can be blended (Manley, 2000).

The chemical changes happens in biscuit include off-flavor and nutritional

deterioration. Development of off-flavor in biscuit as the result of fat oxidation,

usually called as oxidative rancidity. The rate of fat oxidation depends on some

factors includes moisture, certain metal ions, temperature, and light. High

temperature will fasten the fat oxidation, thus reduce the quality of the biscuit. For

the nutritional deterioration, it is affected mostly by temperature. As the

temperature of the storage is high then the rate of the nutritional deterioration will

be fast (Manley, 2000).

One of the parameter to observe whether the biscuit has gone deterioration

process is by the peroxide value. Doncaster et al. (1986) stated that the peroxide

9

value of biscuit will increase as the storage period increased. Allen and Hamilton

(1994) stated that peroxide value has been used as indication for degree of

oxidation. Degree of oxidation sometimes correlates with flavor. As the degree of

oxidation is increasing then the flavor will be decreasing. The oxidation process is

caused by reaction of fat with heat and light that produce free radicals. The

concentration of free radical will be increased until it reaches the critical level and

then it will be propagating; at this stage, the peroxide value will be increasing.

10

CHAPTER III

MATERIALS AND METHOD

3.1 Materials and Equipments

The materials used for this experiment are coconut biscuit, orange juice,

acetic acid, chloroform, saturated KI, 0.1N Na2S2O3, distilled water, starch

indicator, ascorbic acid, metaphosphoric acid, and indophenols solution. While

the equipments used are oven, analytical balance, burette, Erlenmeyer, volumetric

pipette, mortar and pestle, volumetric flask, beaker glass, plastic, and bulb pump.

3.2 Procedure

3.2.1 Sample Analysis

1. The coconut biscuit and orange juice was stored in an oven set at

temperature 400C, 500C, and 600C. For the coconut biscuit, it was sealed

with plastic first.

2. Coconut biscuit was analyzed for the peroxide value and aroma while

orange juice was analyzed for the vitamin C content and flavor.

3. During the storage time, both of the samples were observed based on the

quality parameter.

3.2.2 Vitamin C Content Analysis

1. 5 ml of metaphosphoric acid-acetic acid and 2 ml of orange juice was

added to Erlenmeyer.

2. The solution was then titrated with indophenols solution until the color

changes into light pink color.

3. The indophenols solutions used were recorded.

4. For standardization of dye, 2 ml of ascorbic acid was used in change of 2

ml of orange juice.

5. For blank titration, 2 ml of metaphosphoric acid was used in change of 2

ml of orange juice.

3.2.3 Peroxide Value Analysis

1. 5 grams of sample was put into Erlenmeyer.

11

2. 30 ml of solvent consists of acetic acid and chloroform (3:2) was added to

the Erlenmeyer and mixed.

3. 0.5 ml of saturated KI was added to the solution and shaked for 2 minutes.

4. Then, 30 ml of distilled water was added.

5. The solution mixture was titrated with 0.1N Na2S2O3 until the solution

changes color into light yellow.

6. 0.5 ml of starch indicator was then added until the solution become blue

color.

7. The solution was titrated again with 0.1N Na2S2O3 until the blue color

disappears.

8. The volume of Na2S2O3 used was recorded.

9. Blank solution was titrated with the same procedure.

12

CHAPTER IV

RESULTS AND DISCUSSIONS

Shelf life can be defined as guidance for consumer about time period a

food can be kept before deterioration starts if storage conditions of the products

are followed. During shelf life period, food should be safe during consumption,

retain its appearance, odor, texture and flavor, and meeting declaration of

nutritional claims provided in the label. Changes that can be parameters shelf life

of product can be classified to microbiological, physical and chemical changes. In

this experiment, there are two out of four measurement methods of shelf life used,

sensory evaluation and chemical measurement, while shelf prediction used is by

Accelerated Shelf Life-Testing (ASLT). ASLT principle is that by changing

normal storage condition, thus accelerating deterioration caused by chemical or

physical process and predictive shelf-life relationship related to ambient storage

temperature can be defined. The storage condition in ASLT is raise of temperature

and determined by Arrhenius model since accelerated temperature can lead to

accelerated deterioration. ASLT is applicable to process that has valid kinetic

model and usually most studies of shelf life used based on chemical deterioration

of product. (Kilcast and Subramaniam, 2000).

In this experiment, there are two samples that were assessed in term of

shelf life period, orange juice through the measurement of vitamin C content and

sensory evaluation of flavor and biscuit through measurement of peroxide value

and sensory evaluation of aroma. Each of them was put in varying temperature

40°C, 50°C and 60°C for accelerated shelf life testing (ASLT) for 28 days.

Vitamin C content and peroxide values were examples of chemical measurement,

while scoring of orange juice flavor and aroma were examples of sensory

evaluation methods for shelf life measurement. The design of shelf life

experiment is single batch of product (or replicate batches) is put on test at time

zero with varying temperatures and each samples are taken off for measurement in

each interval of predicted shelf life. The advantage of this design is that it can

13

shows intervals and relationship between time and parameters that can lead to

shelf life determination. The approach for ASLT testing in this experiment is

kinetic model approach, with chemical deterioration order can be either zero or

first order. The order of chemical reaction of each parameters of each samples will

be determined in this experiment with single accelerating factor used in this

experiment, thus Q10 as the ratio between reaction rate and temperature change

(10°C) also determined. Q10 itself is popular method for shelf life determination

(Kilcast and Subramaniam, 2000).

4.1 Shelf Life Determination of Orange Juice

During storage, there are several deterioration reaction which can be

limiting changes of shelf life, such as flavor and nutrient loss as well as cloud

instability. They are caused by several deterioration mechanisms such as

oxidation and enzymatic reaction. Therefore, in this experiment, vitamin C

content as the parameter of nutrient loss and sensory evaluation as the parameter

of flavor loss are done (Kilcast and Subramaniam, 2000).

4.1.1 Measurement of Vitamin C Content

Even tough fruit juice only contain trace amount of vitamin C, however

vitamin C is a major nutritional significance in fruit juice itself in relation to

nutritional value and health claim. Its amount in fruit juice is dependent to

processing method received by the fruit juice, vitamin C is a powerful reducing

agent and easily oxidized to dehydroascorbic acid at elevated temperature during

processing. Besides processing method, vitamin C content of fruit juice also

dependent to storage condition and can be further loss if the container is open to

atmosphere. Vitamin C can be fortified to juice product, aside from vitamin C

content from the fruit itself. Low pH or acidity can help in stabilizing vitamin C

and protect it from further loss. Packaging must be created in order to prevent loss

of vitamin C since it is sensitive to heat and light which can be further catalyzed

by presence of copper ions. Commercial orange juice in this experiment is packed

in tetra pak aseptic carton package. Tetra pak itself is composed of a laminate of

paper, polyethylene, and aluminum foil that can act as oxygen an light barrier,

thus preventing further loss of vitamin C due to oxidation (Arhurst, 1995).

14

In this experiment, commercial orange juices were stored in higher

temperature and measurement method used to determine vitamin C content is

indophenols titration with results is in unit mg ascorbic acid/ml. The results can

be seen in appendix, with order of reaction determined from R2 value can be seen

in Table 4.1. It is shown in the graphs that in the vitamin C content was

decreasing over time and in increasing temperature. Table 4.1. R2 of zero order and first order graphs

R2 Storage temperature

(°C) Zero order reaction First order reaction

40 0.4880 0.5196 50 0.6658 0.7436 60 0.7734 0.9453

Total 1.9272 2.2085 Since the R2 of vitamin C content from first order is bigger than zero order

reaction (2.2085 > 1.9272), therefore it can be decided that the reducing vitamin C

content of orange juice is classified as first order reaction, which is coherent to

theory stated by Yang and Tang (2002) that fruit juice vitamin C degradation

order reaction is the first order. The Arrhenius graph of first order reaction

showing relationship between ln k and 1/T of room temperature (300 K) is shown

In Figure 4.1

Figure 4.1 Graph of ln k versus 1/T of vitamin C The equation obtained from the graph in figure 4.1 then used to calculate

the shelf life of orange juice using vitamin C content as the limiting factor. The

common storage temperature of orange juice is in room temperature (27°C) is

15

determined for shelf life temperature calculation. Vitamin C content deterioration

standard is determined as the half amount of initial vitamin C content during day

0. In calculation, it can be determined that the shelf life of orange juice based on

its vitamin C content is 53 days in room temperature (27°C).

Figure 4.2 ln shelf life time vs temperature plot in vitamin C From equation in Figure 4.2, the Q10 of vitamin Ccan be calculated. Q10 is

the parameter of shelf life used to measure the sensitivity of the product toward

the degradation, in this case is vitamin C content of orange juice. The higher the

slope produced in plot as shown in Figure 4.2, the higher the Q10 produced, thus

the more sensitive the product to deterioration of vitamin C. According to the

calculation shown in appendix, the Q10 result of vitamin C loss in orange juice is

0.95, which is coherent to literature that Q10 of vitamin C content loss in frozen

concentrated orange juice is less than 2 (Open Shelf Life Dating of Food Advisory

Panel, 1979),

4.1.2 Sensory Evaluation of Flavor

Ashurst (1994) stated that same as vitamin C, flavor is also sensitive to

oxygen and heat since the oxidation reaction of fats and oils in fruit juice itself

which can induce rancid flavor of the juice itself, thus causing loss of typical fruit

flavor characteristic. The flavor loss can further accelerated if the packaging is not

permeable to oxygen, thus in the experiment, the usage of tetra pak in commercial

orange juice is appropriate since the packaging can help to prevent oxygen and

light passing through and cause oxidation (Arhurst, 1995). Flavor of orange juice

16

is considered as important parameter for determining the shelf life of apple juice.

In this experiment, sensory evaluation of flavor is determined by hedonic test with

score 1 as the least typical orange flavor of juice, while score 7 as the most typical

orange flavor of juice, which is very acceptable. The result of the taste evaluation

is shown in appendix. From the data, zero order and first order graphs can be

drawn, which give decreasing trend, showing that the rancid taste in commercial

orange juice is gradually increased, which means that the taste of the commercial

orange juice is gradually become less acceptable to the consumer. Table 4.2. R2 of zero order and first order graphs

R2 Storage temperature

(°C) Zero order reaction First order reaction

40 0.4916 0.4517 50 0.8615 0.9161 60 0.6051 0.7413

Total 1.9582 2.1091 Since the R2 of flavor score of orange juice from first order is bigger than

zero order reaction (2.1091 > 1.9582), therefore it can be decided that the flavor

loss process in orange juice is classified as first order reaction. The Arrhenius

graph of first order reaction showing relationship between ln k and 1/T of room

temperature (300 K) is shown in Figure 4.3.

Figure 4.3 Graph of ln k versus 1/T of Flavor

The equation obtained from the graph in figure 4.2 then used to calculate

the shelf life of orange juice using flavor sensory test as limiting factor. The

common storage temperature of orange juice is in room temperature (27°C) is

determined for shelf life temperature calculation. Flavor deterioration standard is

17

determined as the half of highest flavor score of the juice, which is 3.5. In

calculation in appendix, it can be determined that the shelf life of orange juice

based on its orange juice flavor is 156 days in room temperature (27°C).

Figure 4.4 ln shelf life time vs temperature plot of orange juice flavor

From equation in Figure 4.4, the Q10 of orange juice flavor can be

calculated. Q10 is the parameter of shelf life used to measure the sensitivity of the

product toward the degradation, in this case is vitamin C content of orange juice.

The higher the slope produced in plot as shown in Figure 4.4, the higher the Q10

produced, thus the more sensitive the product to flavor loss. According to the

calculation shown in appendix, the Q10 result of flavor loss in orange juice is 0.94,

which is still less than literature’s Q10 of sensory quality loss of frozen

concentrated fruit juices which can vary from 2 to 8. This can happen because the

heat treatment which was functioned to inactivate enzyme, in turn also cause the

flavor changes occur in great extent (Open Shelf Life Dating of Food Advisory

Panel, 1979). However, since the sample is UHT orange juice in tetra pak, the

flavor loss can be still minimized by the packaging itself, since Tetra Pak can act

as barrier of oxygen and heat that can degrade flavor volatiles.

4.1.3 Overall Shelf Life of Commercial Orange Juice

Based on its vitamin C content, the shelf life of commercial orange juice is

53 days at room temperature (27°C), while, based on flavor loss, the shelf life is

156 days at room temperature (27°C). The shelf life based degradation of vitamin

C is shorter than shelf life of orange juice flavor, thus vitamin C is the limiting

18

parameter of orange juice shelf life. Based on this consideration, the overall shelf

life of commercial orange juice is 53 days at room temperature (27°C).

4.2. Shelf Life Determination of Biscuit

4.2.1 Biscuits Aroma

In this experiment, samples of Roma Kelapa biscuit were stored in 40°C,

50°C, and 60°C for 55 days. The aromas of the samples were observed after 0, 5,

19, 33 and 55 days. The aromas were scored in range of 1 to 7. Score 1 means that

the aroma is unusual or rancid. Score 7 means that the aroma is normal. The

aroma is considered unaccepted if the score reach half the maximum score. This

means that the aroma is unaccepted if the score is 3.5 or below. The results of the

biscuit aromas assessments are presented in table 4.3. Table 4.3 Sensory Evaluation of Biscuit Aroma

Based on the results, biscuits stored at lower temperature showed higher

scores than biscuits stored in higher temperature, and as the storage time

increases, the scores are decreasing. The aromas of the biscuit samples stored in

40°C are still acceptable until day 55. While the aromas of biscuits stored in 50°C

and 60°C are still acceptable until day 33. At day 55, the aromas are considered as

unacceptable because the scores are 3.5 and 1.92 that are less than or equal to 3.5.

These unacceptable scores are due to the rancid aroma that is caused by lipid

oxidation, because biscuit is easily become rancid when exposed to oxygen due to

its high fat content (Manley, 1998).

In this experiment, the shelf life of biscuit based on the aroma is calculated

using ASLT (Accelerated Shelf Life Testing) method. By using ASLT method,

first the order of reaction has to be determined. The R2 values for the graphs of

aroma scores are shown in table 4.4. Table 4.4 R2 of zero order and first order graphs

Temperature Day 40oC 50oC 60oC 0 6.91 6.91 6.91 5 7 6.36 4.81

19 6.27 5.45 4.91 33 6.25 4.83 3.92 55 5.58 3.5 1.92

Temperature ( oC) R2 (zero order) R2 (first order) 40 0.966 0.969 50 0.995 0.996

60 0.936 0.948 Total 2.897 2.913

19

From the table, the R2 of biscuit aroma of the first order is bigger than the

R2 of zero order. Therefore, the change in biscuit aroma is considered as first

order reaction. The k values are then calculated and the Arrhenius graph of the

first order reaction is shown in figure 4.5.

Figure 4.5 Graph of ln k versus 1/T of biscuit aroma

From the figure 4.5, the equation of the line is used to calculate the shelf

life (ts) of biscuits based on the aroma. Biscuits are usually stored in room

temperature (27°C). The shelf life of biscuit stored in 27°C is 519 days. Stability

of the biscuit aroma is then calculated by using Q10 formula. The relationship

between ln shelf life and temperature (T) is shown in figure 4.6.

Figure 4.5 Graph of ln k versus T of biscuit aroma

From the equation in figure 4.5, the Q10 is calculated and the result is

0.921. Higher Q10 value means that the food product is less stable. This means that

the aroma of the biscuit sample is quite stable because it has a low Q10 value.

4.2.2 Peroxide Value

20

Peroxide value is the peroxide content in a food product. Peroxide is

related with the rancidity of a product, which is caused by lipid oxidation. Lipid

oxidation produces free radical components that are known as peroxide.

Therefore, the peroxide value can be used as a parameter determining the shelf

lives of products that are easily get rancid (Syarief and Halid, 1993).

In the experiment, the results of the peroxide values for all the biscuit

samples are 0. This might be caused by the samples are stored in sealed plastics.

Thus, the biscuits are not exposed to oxygen and lipid oxidation did not occur.

Since the peroxide values of all the biscuit samples are 0, the shelf life of biscuit

is only determined by the aroma parameter.

21

CHAPTER V

CONCLUSION

In experiment of shelf life determination, Arrhenius method and chemical

kinetics can be used to calculate shelf life of products stored in room temperature

based on its deteriorative reaction in higher temperatures, using sensory

evaluation and measurement of components which are easily degraded as

parameters. It is known that the shelf life of commercial orange juice stored in

room temperature (27°C) is 53 days using the vitamin C as the limiting factor.

Meanwhile, the shelf life of commercial biscuit itself is 531 days stored in room

temperature (27°C) based on sensory evaluation of aroma. The Q10 calculated

from each factors of both products shows that the product is quite stable during

storage condition.

22

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