Thermal-based imaging for detection of Aspergillus niger in onion.

Onion (Allium cepa L.) is a major commercial vegetable crop that plays a vital role in the
agricultural economy, but it is highly prone to post-harvest losses, particularly due to fungal
contamination such as Aspergillus niger, which causes black mold. These losses are often
aggravated by improper handling, lack of grading, and unsuitable storage conditions. Early
detection and proper sorting of infected bulbs are essential to maintain quality and extend shelf
life. The present study focuses on the use of thermal-based imaging as a non-destructive
technique for the detection of Aspergillus niger infection in onions. A large quantity of onion
samples was collected from APMC, Mysore and subjected to grading based on physical
characteristics such as size, external damage, and visible defects. The grading process played
a significant role in segregating visibly affected and healthy bulbs, thereby reducing the risk of
cross-contamination during storage. Thermal images of the collected onion samples were
captured and analyzed to identify variations in surface temperature patterns. These variations
are associated with physiological and microbial activities occurring within the bulbs. The study
successfully identified stable isotherm benchmarks for quality differentiation at 41.0°C for
Nasik onions and 41.5°C for Bijapur onions across all four testing intervals. Data analysis
revealed a consistent correlation of isotherm with the presence of Aspergillus niger in onions.
The isotherm area of 70% or above was identified as healthy onions fit for storage, while area
below 70% served as a definitive marker confirming the presence of Aspergillus niger infection
on the onions. The results indicate that thermal imaging can serve as an effective, rapid, and
non-invasive tool for identifying potentially infected onions at early stages. Additionally, the
study emphasizes the importance of proper grading in minimizing post-harvest losses and
improving storage efficiency. The integration of grading practices with advanced imaging
techniques can significantly enhance quality control, reduce spoilage, and ensure better market
value of onions.