1. Lusani Vhangania* , XabisThysa , Sonia Silabelea & Jessy Vanwyka
ANTOXIDANT AND INHIBITORY EFFECT OF MAILLARD REACTION PRODUCTS (MRPs) AGAINST ENZYMATIC BROWNING OF Granny smith apples
Lusani Vhangania* , XabisThysa , Sonia Silabelea & Jessy Vanwyka
aFaculty of Applied Sciences, Department of Food Science & Technology, Cape Peninsula University of Technology, P.O. Box 1906, Bellville, 7535, South Africa
INTRODUCTION
RESULTS & DISCUSSIONS
Enzymatic browning (EB) is responsible for up to 50% loss of fresh fruits during post-harvest processing1. EB of fresh-cut fruits is a costly problem for the industry due to its adverse effect on appearance, aroma, flavour, and nutritional value, thus reducing the product shelf-life2
The enzyme responsible for browning is polyphenol oxidase (PPO), which catalyzes the oxidation of polyphenols to form coloured melanin.
Sulfites have been used to control browning by acting as reducing agents, they react with quinones to form stable sulphoquinones and inactivate PPO by irreversibly binding to the enzyme3. However, sulfites have been found to destroy thiamine, they are currently restricted due to the allergic reactions in hypersensitive asthmatics. As a result, alternative anti-browning agents should be investigated4
Maillard reaction products (MRPs) formed via amino acid sugar condensation have been proven to inhibit EB through metal chelation, oxygen scavenging and reducing properties5. Therefore, the aim of the study was to determine the antioxidant activity of MRPs and their inhibitory effect against EB of apples
Table 2. Antioxidant activity of Glucose: Casein model systems.
Model system
Antioxidant indices
Temp
(°C)
Time
(h)
DPPH-RS RP
PRS MC 6
50 ± 3.14b
0.03 ± 0.31a
12 ± 4.0 b
36 ± 0.70c 60 12
61 ± 9.00c
0.10 ± 0.34b
20 ± 8.0 c
39 ± 0.71d 24
80 ± 0.00e
0.13 ± 0.19c
19 ± 0.5 c
36 ± 0.71c
75 ± 20.24d
0.16 ± 0.02cd
22 ± 4.2 c
52 ± 0.71e 75
54 ± 2.12b
0.19 ± 0.20cd
23 ± 0.8 c
16 ± 0.00a
0.22 ± 0.30d
23. ± 1.0 c
34 ± 0.71b
Asc acid
86 ± 4.0f
2.00 ± 0.44e
2 ± 0.44a
75 ± 2.14F
EDTA -
27 ± 0.71a
* Data represented as % DPPH and peroxyl radical scavenging activity, metal chelation & reducing power of MRP model systems, ascorbic acid and ethylenediaminetetraacetic acid as mean ± standard deviation (n = 3). ANOVA and Duncan’s multiple range tests were performed. abcdef Means with different letter superscripts within and between columns denote significant differences (p < 0.05).
METHODOLOGY
The DPPH-RS of GC MRPs increased (p < 0.05) as the time increased at 60°C, however, at 75°C a sudden decrease (p < 0.05) was observed. This is due to the complexity of melanoidins formed at this stage. Asc acid exhibited the highest RP compared to MRPs. This is attributed to its ability to act as an excellent reducing agent that donates a Hydrogen atom. On the other hand, MRPS exhibited better PRS than Asc acid. Albeit, MRPs showed lower MC when compared to Asc acid, some (GC 75°C at 6 & 12 h) exhibited higher (p < 0.05) MC activity than the well known EDTA
RESULTS & DISCUSSIONS
Table 1. Non-specific indicators of Glucose : Casein model systems.
Temp
(°C)
Time
(h) pH
reduction
Colour
Measurement L* a* b* 6
7.2 ± 0.2d
45.6 ± 1.0d
-1.4 ± 0.6a
5.8 ± 1.0a 60 12
6.1 ± 3.6c
44.0 ± 0.6d
-0.7 ± 0.9a
10.2 ± 1.7b 24
4.5 ± 0.9a
38.1 ± 2.c
3.3 ± 2.4b
14.9 ± 2.2c
6.9 ± 2.6d
28.1 ± 1.9b
7.0 ± 1.0c
6.3 ± 2.7a 75
5.4 ± 1.3b
25.6 ±1.7b
7.7 ± 2.1c
10.7 ± 0.9b
5.3 ± 2.4b
15.7 ± 0.4a
9.0 ± 1.5d
16.0 ± 2.5c
* Data represented as pH reduction and CIELab colour of MR model systems expressed as mean ± standard deviation (n = 3). ANOVA and Duncan’s multiple range tests were performed. abcdef Means with different letter superscripts within and between columns denote significant differences (p < 0.05).
Figure 1 shows a graph depicting the ability of GC-MRPs in inhibiting EB. Asc acid and EDTA showed the highest efficacy in inhibiting PPO activity. Some GC-MRPs exhibited the ability to suppress PPO activity compared to the control. These results are in agreement with the observation in pH reduction as well as MC activity. GC-MRPs at 60°C, 24 h resulted in a pH of 4.5 which is lower than the range (5-7) required for optimum function of PPO. MRPs (75°C, 6 & 12 h) also exhibited their anti-browning activity via chelating the copper group on the active site of the enzyme.
CONCLUSIONS
As the reaction temperature and time increased, an increase (p < 0.05) on the pH of GC models systems was observed. This results from the formation of acetic and formic acid during the course of the reaction. With reference to colour, the L* coordinates decreased (p < 0.05) with increasing temperature. This is due to the formation of brown melanoidins that occur as the reaction progresses. These compounds intensify with prolonged heating. A similar trend was observed with an increase in the red and yellow component of the a* and b* coordinates, respectively
Although the dip test as observed via ∆E showed that browning od apples was perceivable by the human eye (results not shown), the PPO activity assay opposed this observation. The above results proves that MRPs can be used as alternative antioxidants in food products.
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REFERENCES
Dept. of Food Science & Technology (CPUT), university research fund financial support.
ACKNOWLEDGMENT