Towards Substitution of Hexane as Extraction Solvent of Food Products and Ingredients with No Regrets

Abstract

Hexane is a solvent used extensively in the food industry for the extraction of various products such as vegetable oils, fats, flavours, fragrances, colour additives or other bioactive ingredients. As it is classified as a “processing aid”, it does not have to be declared on the label under current legislation. Therefore, although traces of hexane may be found in final products, especially in processed products, its presence is not known to consumers. However, hexane, and in particular the n-hexane isomer, has been shown to be neurotoxic to humans and has even been listed as a cause of occupational diseases in several European countries since the 1970s. In order to support the European strategy for a toxic-free environment (and toxic-free food), it seemed important to collect scientific information on this substance by reviewing the available literature. This review contains valuable information on the nature and origin of the solvent hexane, its applications in the food industry, its toxicological evaluation and possible alternatives for the extraction of natural products. Numerous publications have investigated the toxicity of hexane, and several studies have demonstrated the presence of its toxic metabolite 2,5-hexanedione (2,5-HD) in the urine of the general, non-occupationally exposed population. Surprisingly, a tolerable daily intake (TDI) has apparently never been established by any food safety authority. Since hexane residues are undoubtedly found in various foods, it seems more than necessary to clearly assess the risks associated with this hidden exposure. A clear indication on food packaging and better information on the toxicity of hexane could encourage the industry to switch towards one of the numerous other alternative extraction methods already developed.

Limonene as a natural product extraction solvent

“…Limonene, furthermore, is nearly entirely recovered after each extraction cycle whereas, like in any other natural product extraction carried out with n -hexane, huge losses of the oil-derived solvent in the atmosphere and in the food chain are recorded every year. 44 In closer detail, the vegetable oil and natural product industries use approximately 1.1 million tonnes of hexane annually (650 kt for oilseed extraction and 450 kt for the production of natural extracts) to compensate for solvent losses during processing. 44 Of this, two-thirds (730 kt) are released into the atmosphere, and one-third (370 kt) remain in the oils and natural extracts.…”

“…44 Of this, two-thirds (730 kt) are released into the atmosphere, and one-third (370 kt) remain in the oils and natural extracts. 44,45 For example, only in the oil extraction from oilseeds losses amount to about 0.3–0.55 kg hexane per tonne of crushed seeds for soybeans and 0–2–0.7 kg t −1 for rape and sunflower seeds (when using the best available technologies, much more with older plants). 45…”

“…On the other hand, volatile organic solvents such as hexane are readily lost in the atmosphere to such an extent that the vegetable oil and natural product industries need 1.1 million tonnes of fresh hexane every year to replace solvent losses. 44,45…”

Limonene as natural product extraction solvent

“…Limonene, furthermore, is nearly entirely recovered after each extraction cycle whereas, like in any other natural product extraction carried out with n-hexane, about two thirds of the toxic solvent is lost in the atmosphere. 36 In the extraction of food ingredients (including oil extraction from oilseeds) with hexane, indeed, the industry needs slightly more than 1 million t of hexane annually to compensate for solvent losses in the atmosphere during processing. 36 A similar conclusion can be reached for valued Gutta-Percha extracted with limonene from leaves, samara, and bark of Eucommia ulmoides, a tree whose excellent natural rubber chiefly composed of trans-1,4-polyisoprene holds large potential application.…”

“…36 In the extraction of food ingredients (including oil extraction from oilseeds) with hexane, indeed, the industry needs slightly more than 1 million t of hexane annually to compensate for solvent losses in the atmosphere during processing. 36 A similar conclusion can be reached for valued Gutta-Percha extracted with limonene from leaves, samara, and bark of Eucommia ulmoides, a tree whose excellent natural rubber chiefly composed of trans-1,4-polyisoprene holds large potential application. 37 Recently, a joint team in China led by Gu reported that using dlimonene at extraction temperatures ranging from 128 °C (for the samara) through 138 °C (for the leaves), excellent yields of high quality Gutta-Percha ranging 81.14 for the samara through 22.15 mg/g for the leaves and 55.32 mg/g for the bark, are readily obtained.…”