Total phenolic content of microwaved, pan-heated and stewed, herbs and spices

Culinary herbs and spices help improve food flavour in cuisine all over the globe and possess some of the richest sources of polyphenols in edible plant foods which are linked to human health benefits. Food processing can affect these constituents and therefore may impact the health benefits these plants may confer. This study aimed to assess the impact of 3 commonly used domestic cooking methods on the total phenolic content, assessed via the total phenolic content (TPC) assay, on 15 culinary herbs and 12 spices, fresh and dried (50 samples total). Herbs and spices uncooked (aqueous extracts), microwaved with water (4 min), pan-heated without medium in a non-stick pan (5, 10, 15 and 20 min) and stewed with water (30, 60 and 120 min) were tested (n = 3) for TPC, expressed in gallic acid equivalent (GAE). TPC for uncooked plants were ranked from very low (below 50 GAE mg/100g) to very high (over 4000 GAE mg/100g). Dried herbs and spices were significantly higher in TPC than their fresh counterparts (P < 0.01). Despite exceptions to the general trend, overall microwaving increased the TPC by 18% compared to uncooked extracts (P < 0.01). Pan-heating in a non-stick pan caused a significant decrease in TPC, averaging 14% (p < 0.01), similar between the 4 lengths of times. Stewing significantly increased the TPC (p < 0.01) by 26% at 30 min, 39% at 60 min and 46% at 120 min. Therefore, polyphenol bioaccessibility in culinary herbs and spices decreased with dry pan-heating but increased with microwaving and stewing with water.