Refractance Window Dehydration Technology: A Novel Contact Drying Method

Abstract

Refractance Window® (RW) system is a novel drying method for converting liquid foods and other related biomaterials into powders, flakes, or sheets with added value. In this system, purees or juices prepared from fruits, vegetables, or herbs dry in short times, typically 3–5 min, resulting in products with excellent color, vitamin, and antioxidant retention. The RW drying systems are simple and relatively inexpensive when compared with freeze drying, which usually needs large installations to be economical. In RW drying systems thermal energy is transferred from hot water to a film of puree or juice spread thinly on a plastic conveyor belt. These drying systems operate at atmospheric pressure and are used for commercial production of scrambled egg mix, avocado powder, high carotenoid-containing algae, herbal extracts and human nutrition supplements, and food ingredients, as well as dried fruits and vegetables. This article presents the principle of Refractance Window® drying and highlights some results that show its potential and how it compares with other dryers for processing fruits, vegetables, and other heat-sensitive products.

Keywords:

• Conveyor dryer
• Drum dryer
• Film dryer
• Fruit and vegetable powders
• Novel drying method
• Nutraceutical
• Quality

Notes

¹RW^TM is a trademark used exclusively for Refractance Window® drying and evaporation. Their mention in this paper is solely for correctness and does not imply endorsement of the technology over other systems performing similar function. Unless otherwise stated, RW will refer to Refractance Window® or RW^TM.

*Heating water temperature;

**Plate temperature; RW: Refractance Window; MWSB: Combined microwave and spouted bed (from Nindo et al.[ ⁴⁵ ]).

L: lightness, a*: redness, b*: blueness, Chroma, C = (a*² + b*²)^1/2, H: tan⁻¹(b*/a*).

^abcd Different letters in the same column indicate significant difference (p ≤ 0.05).

^abcd Different letters in the same column indicate a significant difference (p ≤ 0.05).

*With maltodextrin.

The results are average of three replicates.

^ab Different letters in the same column indicate a significant difference (p ≤ 0.05).

*Process water temperature was 95^oC. Data are means of three replicated tests for each group of microorganisms.