Impact of pre-processing and drying method on the phytochemical content of vegetable baked snacks

Abstract

Phytochemicals are bioactive compounds widely recognised for their potential to help in disease prevention, without being classified as essential nutrients. They, therefore, contribute to the functional food landscape - food that provides additional health benefits beyond its basic nutrition. Though the impact of various drying techniques on phytochemicals has been extensively studied, there is limited research when applied to composite snack foods. This study investigated the influence of the vegetable pre-processing method and drying technique on the phytochemical retention in vegetable snacks. Five snacks were prepared from carrot, onion, parsley, and broccoli in their fresh, frozen, or freeze-dried form, and were dried using either a standard hot-air baking or a hybrid baking (microwave dehydration and hot-air baking in tandem) technique. The glucosinolate, apigenin, quercetin and β-carotene content of the fresh, pre-processed, and finished products were assessed using high-performance liquid chromatography and the percentage difference between the dough and the finished product was calculated. Apigenin glucosides were shown to be most resistant to thermal degradation followed by quercetin glucosides > glucosinolates > and β-carotene. The pre-processing state of the vegetable was shown to have a statistically greater impact on the phytochemical content in the finished product than the baking technique. Hybrid baking was determined to be a less deteriorative processing technique than standard baking, due to microwave power reducing the baking temperatures/times required to obtain snacks of the same moisture content. In particular hybrid baking using fresh vegetables was the best combination for obtaining maximum phytochemical retention.