Overview
Boopathi and co-authors framed agricultural by-products as dynamic multi-hazard matrices rather than passive residues, synthesizing evidence across rice bran, grape pomace, coffee by-products, olive pomace, oilseed cakes, spent grain, and other processing streams. The review covers heavy metals, mycotoxins, pesticides, polycyclic aromatic hydrocarbons (PAHs), mineral oil hydrocarbons (MOHs), and allergens. For heavy metals, inorganic arsenic in rice bran and lead in grape pomace are the most clearly documented concerns relative to regulatory benchmarks for food ingredients.
Key numbers
Rice bran, inorganic arsenic (inorganic arsenic):
| Measurement | Reported value |
|---|---|
| Commercial raw rice bran, inorganic arsenic (iAs) range | 376 to 1079 micrograms/kg |
| Commercial raw rice bran, median inorganic arsenic (iAs) | 601 micrograms/kg |
| EU infant rice ML (reference limit) | 100 micrograms/kg |
| EU polished rice ML (reference limit) | 150 micrograms/kg |
| Codex polished rice ML (reference limit) | 200 micrograms/kg |
| FDA infant rice cereal ML (reference limit) | 100 micrograms/kg |
| Percolation cooking (300:1 water-to-bran), median inorganic arsenic (iAs) after treatment | 167 micrograms/kg |
| Median inorganic arsenic (iAs) removal by percolation cooking | 76% |
Rice bran inorganic arsenic at 376 to 1079 micrograms/kg is 3.7 to 10.8 times the EU and FDA infant food limit of 100 micrograms/kg, and 1.9 to 5.4 times the Codex polished rice limit of 200 micrograms/kg.
Grape pomace flour, selected metals:
| Analyte | Reported range | Reference benchmark |
|---|---|---|
| Total arsenic | 100 to 360 micrograms/kg | EU fruit benchmark: varies by fruit; 100-360 is in the monitoring range |
| Cadmium | 250 micrograms/kg | EU grape/fruit benchmarks: 50 micrograms/kg or lower |
| Lead | approximately 5000 micrograms/kg | EU fruit benchmark: 100 micrograms/kg |
| Mercury | 4 micrograms/kg | low |
Grape pomace flour lead at approximately 5000 micrograms/kg is approximately 50 times the EU 100 micrograms/kg benchmark for fresh fruit. The review frames lead as intake-limiting for grape pomace flour ingredients.
Strawberry processing by-products, lead: Below 76 micrograms/kg in the data reviewed, below the EU strawberry benchmark of 100 micrograms/kg.
Coffee pulp flour, cadmium: 25 to 61 micrograms/kg, below EU coffee cadmium benchmarks.
Other matrices: PAHs and MOHs are the primary documented concerns for olive pomace, wheat bran milling fractions, and oilseed cakes; heavy metals are present but are not the leading hazard for those matrices in the evidence reviewed.
Methods (brief)
Systematic literature review and synthesis across multiple by-product categories. Table 8 consolidates metal data for rice bran and other matrices with regulatory benchmark comparisons. Table 10 provides an integrated multi-hazard framework across by-product types. No primary experimental measurements; all values are drawn from cited primary studies.
Evidence fitness
Supports: rice bran as a high-inorganic arsenic matrix well above infant food MLs; grape pomace flour as a high-lead matrix well above fresh fruit benchmarks; mitigation context for rice bran (percolation cooking reduces inorganic arsenic by approximately 76%). Does not support: individual source citations without tracing back to primary studies; a single definitive value for any matrix without reading the contributing primary literature.
Limitations
Systematic review synthesizing heterogeneous primary literature. Rice bran values draw on a limited set of commercial samples from studies reviewed; range reflects between-study and between-sample variation. Grape pomace lead at approximately 5000 micrograms/kg is an extreme value within the reviewed literature; the review’s table documents this but does not perform a formal meta-analysis. Regulatory benchmarks compared are for fresh fruit or polished rice, not for by-product-derived food ingredients, for which specific MLs often do not exist.
Related evidence
Update history
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