The effect of intense pulsed light on the sensory properties of milk powder and wheat flour and The two-out-five test compared to the triangle test in terms of sensory adaptation, test sensitivity, and selective attention

Abstract

Intense pulsed light (IPL) treatment is an emerging technology that has the potential to be used for decontaminating foods as an alternative to thermal processing (Mandal et al., 2020). Researchers (Kramer et al., 2017b; Mahendran et al., 2019; Oms-Oliu et al., 2010) have investigated the feasibility of adapting IPL processing to the food industry to address increasing outbreaks of life-threatening diseases in low-moisture products (e.g., dry milk powder, powdered infant formula, whey powder, wheat flour, and spices). To apply this novel technology at the commercial level, food manufacturers need to develop an optimized IPL system that effectively reduces microorganisms without sacrificing the sensory properties of treated products. Thus, we investigated how IPL processing parameters affected the sensory properties of milk powder and wheat flour. Furthermore, we examined the possible benefits of IPL treatment’s less damaging effect on the sensory properties of treated products compared to conventional Ultraviolet light (UV) treatment. Chapter 1 introduces the principle of IPL treatment and photo-oxidation mechanisms as well as previous studies on light-induced sensory or physicochemical changes in milk products and wheat flour. Chapter 2 presents our experimental study on milk powder. We determined how temperature and exposure time affected the sensory properties of non-fat dry milk while determining at which levels these processing parameters produce sensory differences from the untreated sample. Chapter 3 presents the application of IPL for wheat flour. We determined the effects of IPL processing parameters (voltage, feed rate, and frequency) on the sensory properties of wheat flour. Furthermore, we compared the effect of IPL treatment on the sensory properties of treated samples with those of UV treatment at equivalent efficacy in reducing microorganisms.While examining the IPL and UV treatments, we used the two-out-of-five test method instead of the conventional triangle test. In the two-out-of-five test, judges are presented with five coded samples, two of one product and three of the other. The judges are instructed to sort the samples into two groups according to their similarity. By contrast, the triangle test presents the judges with three samples ‒ two samples of one product and one of the other ‒ and the judges are asked to identify the odd sample among the three. We selected the two-out-of-five test because it requires a small number of participants compared to the triangle test. This is due to the low guessing probability of the two-out-of-five tests (⅒) relative to the triangle test (⅓). However, despite this benefit, there has been a long-standing assumption that the multiple tastings in the two-out-of-five test induce memory load and extreme sensory adaptation, consequently deteriorating the judges’ discrimination ability compared to other tests including two or three samples (Lawless & Heymann, 2010; Meilgaard et al., 2015). Since this assumption has been made without experimental demonstration, we were interested in whether the judges’ discrimination performance would, in fact, decrease in the two-out-of-five test compared to the triangle test. This concern inspired the investigation of the two-out-of-five test, as covered in chapters 4 and 5. Chapter 4 reviews the previous use of the two-out-of-five test in sensory research and the potential adverse effects of multiple tastings on taste adaptation and memory load. Additionally, this chapter reviews the role of selective attention in categorization tasks with visual stimuli as a potential advantage of the two-out-of-five test. Chapter 5 presents our experimental research, where we investigated whether the two-out-of-five test elicited greater taste adaptation and a greater proportion of discriminators compared to the triangle test. In addition, to determine the effectiveness of selective attention in taste perception, we compared the number of attributes used by judges to discriminate among samples between the two-out-of-five test and the triangle test and examined if the use of a single attribute improved judges’ discrimination performance.