Saturated steam pasteurization improves nut preservation.

A thesis published in 2023 by the Walnut Board of California demonstrates the positive effect on rancidity and vitamin E content of batch treatment.  They compared saturated steam, continuous heat treatment & no treatment at all.

The 2 systems studied are: the NAPASOL system and a continuous thermal system.

– Saturated steam batch pasteurisation vs. continuous pasteurisation: Batch pasteurisation of nuts offers advantages over continuous pasteurisation. Batch pasteurised nuts show a slower reduction in tocopherols (vitamin E) and a slower accumulation of oxidative by-products. Under these conditions, walnuts exhibited superior sensory attributes compared to those stored in ambient air.

Also, this study was carried out on walnuts preserved in packaging in the absence of oxygen.

-Storage in a low-oxygen atmosphere:  When pasteurized nuts were stored in low-oxygen conditions, lipid peroxidation product (PV), hexanal accumulation & tocopherol degradation, were reduced. Walnuts stored under these conditions scored higher in terms of sensory attributes than those stored in ambient air.

The conclusion is clear: the NAPASOL system, combined with oxygen-free preservation after pasteurisation, provides significantly better preservation vs a continuous treatment system also combined with oxygen-free preservation after pasteurisation.

The study also shows that the use of NAPASOL saturated steam pasteurisation combined with preservation without oxygen preserves the quality of the nuts much better than in the case of untreated nuts simply preserved without oxygen.

These findings, specific to walnuts, may apply to many other nut families with similar characteristics and free fatty acid degradation leading to rancidity.

Link to article :

Nuts treated with saturated steam keep better.