Introduction: Rice is a staple food for over half of the global population and stands as the second most consumed food product in Iran. Its production is increasing, particularly in Khuzestan province, which nonetheless confronts significant challenges in the post-harvest process. Many rice mills employ traditional technologies that result in substantial losses during the conversion of paddy to white rice, consequently escalating overall costs. These losses inflict considerable economic damage on farmers, and mitigating them-especially given limited water resources- is crucial for boosting domestic output and reducing import dependency. The milling stage, encompassing husking and whitening, is the most sensitive, accounting for the highest rate of grain breakage, which directly affects the product’s economic value. The quality of milled rice, quantified by its whiteness degree, is highly valued in Iran, where the recovered head rice yield is the most critical determinant of paddy price. Modern technologies, such as abrasive whiteners, demonstrate superior efficiency compared to traditional systems, capable of minimizing waste and grain breakage. This research investigates the performance of dominant conversion systems in Khuzestan and proposes practical solutions for waste reduction by focusing on key technical parameters.

Materials and Methods: This study aimed to investigate and compare rice conversion systems operating within Khuzestan province. Three distinct rice milling conversion systems were selected: Type A (Conventional), comprising a grain cleaner, a blade-type husker, two parallel blade whiteners, and a grader; Type B (Simple Imported), consisting of a destoner, grain cleaner, rubber roller husker, paddy separator, abrasive whitener, and polisher; and Type C (Advanced Imported), similar to type B but equipped with two serial abrasive whiteners. The specifications and processing stages of their equipment were examined. Paddy samples of the Anbarbo, the region’s dominant cultivar, were dried to a moisture content of 8.9%, then divided into three batches and processed in the three type mills under study. Sampling was conducted at the output of various machines, and system evaluation parameters, including impurity levels, husking percentage, breakage, conversion efficiency, head rice percentage, whiteness degree, and cooking quality properties, were analyzed in the laboratory. The experimental design followed a randomized complete block design with three treatments and three replications. Data analysis was performed using MSTATC software, employing Duncan and LSD tests at a 5% significance level. This rigorous approach ensured accurate evaluation and comparison of the different milling systems to provide actionable solutions for process improvement and waste reduction.

Results and Discussion: Rice mill type C exhibited the lowest impurity levels due to its two-stage grain cleaning process. Rice mill type A, utilizing the blade-type whitener, registered the highest breakage rate, whereas mill type C with its abrasive system yielded the lowest breakage. The use of abrasive systems is recommended for starchy texture cultivar. No significant difference was found in conversion efficiency among the mills, suggesting either improper use or inappropriate settings of the imported systems for local cultivars. Conversion efficiencies for mills A, B, and C were 67.1%, 68.2%, and 66.8%, respectively. Mills B and C, equipped with polishers, achieved a higher degree of whiteness compared to mill A. The type of mill had no significant effect on amylose content, gelatinization, or grain elongation ratio. The amylose percentage in rice from mills A, B, and C was 22.4%, 21.2%, and 22.1%, respectively. Amylose content significantly influences the physical and chemical properties of rice, ultimately affecting its quality and suitability. The gelatinization degree for rice from mills A and B was 4.6, while it was 4.7 for type C. The grain elongation ratio after cooking was 1.7 for type A and 1.8 for the other two types. Based on these results, utilizing mills B and C for processing the Anbarbo cultivar and similar cultivars in Khuzestan province is preferable to traditional mills. Therefore, for processing Anbarbo rice in this region, the use of rubber roller huskers and abrasive whiteners is recommended over blade huskers.

Conclusion: This research investigated the effect of rice mill type on the quality and quantity of rice in Khuzestan province. The results indicated that the type of mill significantly impacts paddy impurity levels, rice breakage, and the degree of whiteness, whereas conversion efficiency and other key quality characteristics of rice remained unaffected. Mills equipped with superior machinery, such as two-stage grain cleaners and abrasive whiteners, yield higher quality rice. Therefore, the correct selection of rice milling equipment, particularly huskers and whiteners, is crucial for improving rice quality and reducing waste. Specifically, the use of rubber roller huskers is recommended for processing the Anbarbo cultivar.