Abstract
This PhD research investigates the effects of sustainable technologies such as microwave
(MW) and ultraviolet (UV) technologies on mycotoxins decontamination in rice. Rice is a staple
food crop globally. However, rice is prone to mycotoxin contamination due to improper pre and
post-harvest handling. Mycotoxin contamination of rice has significant economic and
public health implications, compromises food safety and reduces food quality.
Insights into mycotoxins contamination of rice were investigated using bibliometric
analysis and meta-analysis of published literature. The study found a growing interest in the
research area of mycotoxins decontamination, with China and the United States being leading
contributors. The keyword analysis showed that the keywords were related to mycotoxins
production, analytical techniques, and emerging mycotoxins. The newest research terms were
food safety, decontamination, dietary exposure, and detection using immunoassay and
aptamers. Meta-analysis of 62 articles with 408 studies showed a 15 % (95 % CI: 12-17 %)
global prevalence of mycotoxins in rice. The global overall mycotoxins concentration in rice
was 18.70 μg/kg. Aflatoxins ranked first for the highest prevalence of mycotoxins in rice.
Europe (44 %) had the highest prevalence of mycotoxins in rice, followed by Africa (32 %).
The highest concentration of mycotoxins is observed in Africa (32.14 μg/kg), followed by Asia
(17.01 μg/kg).
In this study, AFB1 (aflatoxin B1), AFT (total aflatoxin) and OTA (ochratoxin A) were
used in mycotoxins decontamination study due to their highest prevalence in rice. Rice (red
raw) was artificially contaminated with AFB1, AFT and OTA separately. The contaminated
rice was subjected to MW heating at different power levels (560 W, 640 W and 720 W) and
application times (120 and 360 s). The treatment conditions for the UV were 0.5 hr, 1 hr, 2 hr,
3 hr and 4 hr. The effects of MW and UV on mycotoxins degradation were analysed. After the
treatments, the thermal, functional, pasting, cooking, antioxidant, in-vitro starch digestibility,
and nutritional properties of the treated rice were examined.
The results show that the highest MW treatment (720 W, 360 s) reduced the AFT, AFB1,
and OTA by 40.00, 49.31, and 73.39 %, respectively, in rice. However, the lowest MW power
and treatment time (560 W, 120 s) showed significant reductions of AFT (33.40 %), AFB1
(50.06 %), and OTA (75.24 %) in rice. UV treatment significantly lowered mycotoxin content,
with optimal reductions observed after varying exposure times depending on the specific toxin.
The highest reduction in AFT (31.09 %), AFB1 (44.33 %), and OTA (59.96 %) were observed
after 0.5 hr, 4 hr, and 2 hr UV exposure, respectively.
During MW treatment, temperature increased, and the maximum temperature achieved
was 65.66 ◦C and moisture content reduced from 12.20 to 11.20 %. The highest MW treatment
significantly changed the starch morphology. However, no significant (p>0.05) changes in the
crystallinity of the starch were observed. Changes in the secondary structure of the rice proteins
were observed in amide I and II bands in FTIR spectra. Differential scanning calorimetry (DSC)
revealed that MW treatment had no impact on the thermal properties of rice flour. MW
treatment reduced the colour parameters, functional and pasting properties. MW treatment
increased the water/ oil absorption capacity of rice flour and reduced the water absorption index
and swelling power, and these observations were attributed to changes in starch properties. The
peak viscosity, final viscosity, breakdown viscosity and setback were reduced during MW
treatment. The antioxidant activities of rice were reduced significantly (p<0.05) due to a
reduction in total phenolic compounds and total anthocyanin content, specifically when high
MW power 760 W was applied. Additionally, the apparent amylose content and in-vitro starch
digestibility were significantly (p<0.05) reduced with MW radiation. Nevertheless, the MW
treatment improved the cooking time (p<0.0001) and texture properties (p<0.05) of cooked rice.
UV treatments did not significantly (p>0.05) affect the thermal, colour properties, water
solubility index, swelling power, and pasting temperature of the rice flour. Water and oil
absorption capacity were increased after 2 hr of UV treatment. The moisture content and pasting
viscosities were reduced significantly (p<0.001) after UV treatment. Total phenolic content,
total anthocyanin content and total antioxidant activity significantly (p<0.001) reduced after the
UV treatments. The amylose content and in-vitro starch digestibility were significantly (p<0.01)
reduced with 0.5 hr UV treatment time. Cooking time was reduced from 51.33 to 24.67 min
with UV treatment.
Even though ATF, AFB1 and OTA were not completely degraded, MW treatment (560
W, 120 s), and UV exposure for 0.5 hr can be suggested for mycotoxin decontamination without
adversely affecting the rice properties.