Tempeh, a fermented soybean-based food originally from Indonesia, is a remarkably nutritious functional food with health benefits. Unfortunately, tempeh is highly perishable, with a shelf life of 24 – 48 hours. The goal of this research was to evaluate the possibility of a sub-supercritical CO2 technique to increase the shelf life of tempeh by measuring the changes in the
At present, consumers demand fresh food that is not only of high quality and safe but also has a long shelf life. Highpressure carbon dioxide (HPCD) technology has been developed as a food processing technology with the advantage of minimizing the loss of heat-sensitive nutrients. Carbon dioxide in the supercritical state has the dual properties of a gas with high diffusivity and a liquid with high solubility (
Tempeh is an Indonesian fermented food made from soaked, hulled and cooked soybeans inoculated with the fungus
The shelf life of tempeh stored at 20, 30, and 40 °C can be extended by treatment with CO2 at sub-supercritical pressure.
Tempeh, in the form of a cylinder with a diameter of 35 mm and a length of 100 mm, fermented for 36 hours at 30 °C, was obtained from the Center of Home Industry Tempeh Making Palembang, Indonesia, placed in a cooler box and carried to the laboratory for direct processing (
The high-pressure CO2 installation used for experimental treatments, consisting of a CO2 gas cylinder, a cylindrical pressure chamber, pressure gauges, and a water bath at a constant temperature, is shown in Figure
The set-up of the experimental apparatus (Saputra, 2006).
Tempeh processed with sub-supercritical CO2 (6.3 MPa, 25 °C for 10 minutes) and unprocessed tempeh were employed as the treatment and control, respectively, in this experiment. All of the tempeh was stored for 5 days. Tempeh was stored as follows: tempeh samples were placed on a Styrofoam plate and covered with plastic film then stored at 20, 30 and 40 °C with the same relative humidity. Observations on quality parameter changes (
The Accelerated Self Life Test (ASLT) with the Arrhenius model was used to determine the shelf life of tempeh, in which, if the food product deteriorates faster, then the shelf life is determined based on extrapolation to storage temperature. Changes in the quality factor were used to determine the degree of decrease in quality. Data were transformed into a kinetic plot, and an appropriate kinetic parameter model was obtained. The quality decrease in food is given by equation (
Where:
Most of all, a decrease in food quality includes zero-order (order 0) and first-order (order 1) reactions. The Arrhenius correlation chart was generated by evaluating the rate constant (
Where:
The zero-order and first-order quality reaction was measured by using equation (
Where:
The surface colour analysis of tempeh was evaluated as the CIE
The total colour difference (Δ
Where: Δ
The texture analysed was tempeh hardness. The greater the value, the harder the sample being analysed. The LFRA Texture Analyzer (Brookfield AMETEK CT3-100-115), type A 7.1 was used to measure tempeh texture. The texture of the tempeh in this study was the quality of compactness of tempeh when sliced, because compact and dense soybean strands produce tempeh that is easily sliced. Tempeh has a non-homogeneous texture because it consists of woven soybean seeds arranged mycelia. This arrangement gives rise to varying angles/areas of penetration of the probe, for example, the possibility of probes piercing right into the soybean seeds or the soft areas between soybeans strands. Therefore, a Brooke-type probe blade was used in this study. The Brooke-type blade presses right in the centre of the sample. The peak load and final load numbers in units of gram force (gf) listed on the display were recorded. Measurements were performed in three replicates.
Statistical analysis was carried out using Microsoft Excel 2003 and Statistica 8.0 StatSoft software. Analysis of variance (ANOVA) was used to study differences between samples. A software program using Duncan’s multiple range test was used to compare treatment means. A value of
Processed and unprocessed (control) tempeh were used as the models in this experiment. Colour is very important to the sensory nature of tempeh because it is the first characteristic observed by the consumer. The colour of tempeh produced by the growth of mould was influenced by changes in the chemical composition of the tempeh and storage temperature. The lightness (
The lightness (
20 °C | 30 °C | 40 °C | ||||||
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Day |
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Texture | Day |
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Texture | Day |
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Texture |
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0 | 74.6 ±0.06 |
577 ±0.1 |
0 | 74.4 ±0.05 |
577 ±0.3 |
0 | 74.6 ±0.05 |
577 ±0.2 |
1 | 74.1 ±0.07 |
580 ±0.2 |
1 | 73 ±0.050 |
579 ±0.1 |
1 | 69.3 ±0.06 |
701 ±0.2 |
2 | 73 ±0.02 |
585 ±0.1 |
2 | 71.5 ±0.03 |
610 ±0.1 |
2 | 62.3 ±0.06 |
789 ±0.3 |
3 | 71.4 ±0.03 |
589 ±0.1 |
3 | 69.3 ±0.06 |
625 ±0.3 |
3 | 58.2 ±0.06 |
860 ±0.23 |
4 | 70 ±0.03 |
592 ±0.3 |
4 | 68.4 ±0.06 |
660 ±0.3 |
4 | 56 ±0.05 |
870 ±0.4 |
5 | 69 ±0.10 |
593 ±0.3 |
5 | 66 ±0.07 |
690 ±0.2 |
5 | 55.5 ±0.07 |
885 ±0.1 |
Note: All values are the mean and standard deviation of three replicates. a-d Means within a column with different letters were significantly different (
The lightness (
20 °C | 30 °C | 40 °C | ||||||
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Day |
|
Texture | Day |
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Texture | Day |
|
Texture |
|
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0 | 75.3 ±0.11 |
505.7 ±1.0 |
0 | 75.3 ±0.09 |
506 ±0.09 |
0 | 75.3 ±0.9 |
505.5 ±0.1 |
1 | 70.8 ±0.58 |
346.5 ±1.0 |
1 | 74.2 ±0.08 |
396 ±0.05 |
1 | 69.5 ±1.0 |
1233 ±0.09 |
2 | 66.7 ±0.11 |
332 ±0.9 |
2 | 69.5 ±0.1 |
286 ±0.1 |
2 | 65.2 ±1.1 |
1321 ±0.04 |
3 | 63.2 ±0.12 |
338 ±0.9 |
3 | 65.7 ±0.12 |
305 ±0.1 |
3 | 60.7 ±1.2 |
1442 ±0.04 |
4 | 59.5 ±0.09 |
340 ±0.7cd | 4 | 60.4 ±0.11 |
290 ±0.09 |
4 | 55.3 ±1.1 |
1467 ±0.02 |
5 | 58 ±0.09 |
300 ±1.0 |
5 | 57 ±0.8 |
277 ±0.1 |
5 | 54 ±0.9 |
1511 ±0.02 |
All values are the mean and standard deviation of three replicates. a-d Means within a column with different letters were significantly different (
The data obtained from the experiments were plotted on a graph of the relationship between the degradation in the quality of
Evaluation of the linear regression equation for the estimated shelf life of tempeh.
Quality parameters | T, °C | Zero order |
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First order |
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20 | y= -1.197x+75.01 | 0.982 | y=0.0167x+4.318 | 0.981 | ||
30 | y= -1.657x+74.57 | 0.990 | y=0.0236x+4.312 | 0.988 | ||
40 | y= -3.985x+72.61 | 0.919 | y=0.0625x+4.287 | 0.933 | ||
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Texture | 20 | y=3.428x+577.4 | 0.970 | y=0.0059x+6.359 | 0.969 | |
30 | y=23.51x+564.7 | 0.959 | y=0.0375x+6.339 | 0.965 | ||
40 | y=60.51x+629.0 | 0.877 | y=0.0821x=6.443 | 0.847 | ||
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20 | y=-3.54x+74.43 | 0.983 | y= -0.0537x+4.313 | 0.989 | ||
30 | y=-3.906x+76.78 | 0.980 | y= -0.059x+4.347 | 0.975 | ||
40 | y=-4.388x+74.31 | 0.981 | y= -0-069x+4.314 | 0.986 | ||
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Texture | 20 | y=-29.76x+434.7 | 0.581 | y=0.0757x+6.061 | 0.615 | |
30 | y=-41.25x+446 | 0.722 | y= -0.111x+6.090 | 0.745 | ||
40 | y=167.1x+828.6 | 0.687 | y= -0.174x+6.634 | 0.599 |
Figure
The correlation between lightness (
The hard texture of tempeh increased significantly during storage (
The influence of temperature on the reaction rate was described using the Arrhenius equation. The regression equation and value of the R2 data for tempeh at 20, 30 and 40 ℃ are shown in Table
Regression equation of tempeh stored at 20, 30 and 40 °C.
Quality parameter | T, °C | Regression equation | Reaction order | Ea, |
K, |
R2 | Co |
Shelf -life (days) | |
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20 | LnK= -6177.2x+16.839 | First | 0.292 | 2.43 | |||||
30 | 12.27 | 0.145 | 0.923 | 5.1 | 4.88 | ||||
40 | 0.758 | 9.36 | |||||||
20 | LnK= -12883x+38.85 | First | 0.938 | 8.60 | |||||
30 | 25.59 | 0.218 | 0.950 | 48 | 3.67 | ||||
40 | 0.559 | 1.42 | |||||||
20 | LnK= -1206.8x+1.1719 | First | 0.053 | 3.33 | |||||
30 | 2.40 | 0.060 | 0.984 | 9.6 | 2.90 | ||||
40 | 0.068 | 2.56 | |||||||
20 | LnK= -3827.6x+10.458 | First | 0.073 | 6.89 | |||||
30 | 7.60 | 0.113 | 0.995 | 201 | 4.47 | ||||
40 | 0.169 | 2.99 |
Note: 1) Activation energy in kcal.mol-1; 2) Rate constant; 3) Initial value of quality parameter; 4) Data of quality parameter as t time passes; 5) Processed tempeh; 6) Control (unprocessed tempeh).
All food expiration dates could be established as selfapplied safety factors by each producer. For tempeh, expiration dates may not be mandatory because tempeh categorized as a fresh food product has a very short shelf life, and the spoilage of tempeh is easily detectable by looking at the colour, texture and aroma. Therefore, an expiration date is not necessary. From the point of view of microbial safety, tempeh, fermented soybean, is a reliably safe food because bacteria, yeasts and moulds that grow in tempeh have their own specific role.
Sub-supercritical CO2 processing at 6.3 MPa for 10 min increased the shelf life of tempeh at a storage temperature of 30 °C. The shelf life of processed tempeh was 2.43 days at 20 °C, 3.7 days at 30 °C and 1.4 days at 40 °C, and the shelf life of unprocessed tempeh was 3.33 days at 20 °C, 2.90 days at 30 °C and 2.56 days at 40 °C.
This article was presented in PATPI-SEAFAST International Conference: "SCIENCE-BASED INGREDIENTS: THE FUTURE FOR FOOD IN ASIA", °Ctober 3-5, 2018, Indonesia.
The manuscript was first edited and submitted during the Sabbatical Leave of the corresponding author at Mie University, Faculty of Bioresources in the laboratory of Bioinformatics and Food Engineering (BIFE) in 2019 funded by The Ministry of Research, Technology, and Higher Education of the Republic of Indonesia