A Pilot Study on Sensory Evaluation of Commercial Yogurt Products by Italian Middle School Pupils ^†

Abstract

This article reports on a pilot experiment conducted on STEM teaching (Science, Technology, Engineering, and Mathematics) within the context of orientation teaching, wherein young pupils take on the role of “young researchers”. Twenty-six pupils participated in this research, and 18 of them evaluated 20 commercial yogurts (banana, vanilla, strawberry, and plain yogurt). They assessed acidity, sweetness, odor, texture, taste, and overall acceptability using a 5-point scale. Data were analyzed through non-parametric tests, box-whisker plots, and Principal Component Analysis. Statistics point out that for teenagers, overall acceptability was directly related to sweetness (0.695), odor (0.587), and taste (0.861), and indirectly related to acidity (−0.517). In addition, non-parametric tests show high variability within the dataset, with a non-normal distribution of sensory scores.

1. Introduction

Consumer interest in functional foods is growing significantly in the food market landscape, with consumers becoming increasingly health-conscious and increasing their demands for healthier foods [1]. Yogurt consumption, in particular, offers consumers a wide range of choices in terms of availability, variety, tastes, and flavors, and its popularity has increased around the world because of its nutritional value, therapeutic effects, and functional properties [2].

Several studies have confirmed that yogurt has positive effects on human health, reducing the risk of disease [3,4]. In fact, it has been observed that yogurt consumption helps treat diseases including obesity, allergies, intestinal tract inflammation, colon cancer, cardiovascular disease, and Helicobacter pylori infection [5,6,7,8,9,10].

Furthermore, yogurt is easily digestible because milk protein, fat, and lactose components undergo partial hydrolysis during fermentation, making the product extremely accessible to children from an early age. This is also because it has high nutritional value, and is a rich source of carbohydrates, protein, fat, vitamins, calcium, and phosphorus [11].

Consumers are becoming more careful when choosing products to buy, with wholesomeness, safety, and functionality as the main parameters of choice. Flavor is a key factor for foodstuff acceptability [12], with available evidence suggesting a marked preference for fruity yogurts [13]. The introduction of various fruit-flavored yogurts has significantly contributed to the consumption of yogurt across all ages [12].

Nowadays, yogurt has entered the homes of almost all Italians. In fact, since 2010, 99% of Italian families have bought yogurt throughout the year, averaging once every 12 days. This figure, already present in the literature [14], was confirmed by a recent survey carried out in early 2023 [15].

Younger consumers and adolescents, regardless of gender, consider yogurt a preferred food choice to stop mid-morning or afternoon hunger, pairing it with coffee or crackers. They are considered heavy consumers of yogurt and fermented milks, making up an important segment of consumers. These consumers are increasingly influenced by advertising messages, attracted to fashions, and stay in line with current trends. They are also particularly attentive to the quality and safety of products, displaying characteristics such as innovation, informativeness, cultural sensitivity, international cultural awareness, high activity levels, sociability, attentiveness to emotions and feelings, and decision-making abilities [16].

Although many studies have explored the positive factors registered by the consumption of yogurt in relation to the health and well-being of children and adolescents [5,6,7,8,9,10], little is known about their tastes in relation to these products and the factors influence their choices in purchasing functional foods, particularly yogurt.

On the basis of these considerations, scientific research was designed within a project on the teaching of STEM (Science, Technology, Engineering, and Mathematics).

This pilot study was conducted in a synergistic way, by the DAFNE Department of the University of Foggia (Department of the Science of Agriculture, Food, Natural Resources, and Engineering) and the Comprehensive Institute “Foscolo-Gabelli”, an Italian middle school in Foggia (Italy). The study aims to increase the pupils’ degree of knowledge on functional foods, and clarify adolescents’ perspectives on the consumption of yogurt, by outlining the choices and motivations that underlie the purchase of the product by means of sensory evaluations of commercial yogurts in terms of acidity, sweetness, odor, texture, taste, and overall acceptability.

This is certainly the first study in pedagogy and orientation teaching, in which young pupils take on the role of “young researchers” by conducting the entire scientific study alongside industry professionals in order to evaluate the development of specific skills in the technical–scientific field.

2. Materials and Methods

2.1. Pupils, Framework, and Planning Process

This study was conducted by 26 pupils attending the third classes of an Italian middle school (Comprehensive Institute “Foscolo-Gabelli” in Foggia, Italy); their Science and Technology teachers acted as supervisors.

The pupils, based on their personal attitudes towards mathematical–scientific disciplines, freely chose to participate in the “Laboratorio di Math 2”, a 30 h on Science and Technology course, which was part of a grant from the National Operational Program (Italian PON) of the Ministry of Education and Merit (project 10.2.2A-FSEPON-PU-2021-125). The focus of the project was on STEM teaching (Science, Technology, Engineering, and Mathematics) and was supervised by the DAFNE Department of the University of Foggia.

The course was divided in two parts: (i) preliminary training on functional foods (lectures); and (ii) a panel test and sensory evaluation on commercial yogurts.

2.2. Preliminary Training on Functional Foods

In the first part of the project, all 26 pupils, after an initial assessment on basic skills and prerequisites in Science and Math necessary for the subsequent course, attended a preliminary training course organized into 10 lessons, each lasting three hours.

These lessons were structured to provide specific information and broaden knowledge on functional foods, specifically yogurt. The course covered the composition, functional properties, and sensory analysis of yogurt, how to set up a panel test, and how to collect, analyze, and represent statistical data. Furthermore, laboratory lessons on the microbiological analysis of yogurt, the preparation of a panel test on yogurt and fermented milks, and guidance on how to write a scientific paper in English, were planned.

All components of the training course were performed by their Science and Technology teachers and professors from the DAFNE Department of University of Foggia, using the CLIL methodology (Content and Language Integrated Learning).

2.3. Panel Test and Sensory Evaluation of Commercial Yogurt

2.3.1. Preliminary Survey

In the second part of the project, all pupils, on the basis of the knowledge and skills acquired during the initial training course, conducted a survey to find out which yogurt brands were present and sold most in the local market. The 26 pupils were divided into two groups: group A (8 pupils) and group B (18 pupils).

2.3.2. Samples

The pupils of group A identified 20 samples of yogurt, referring to 7 brands and 4 flavors, to be subjected to a panel test aimed at evaluating sensory properties, in terms of acidity, sweetness, odor, texture, taste, and overall acceptability.

Commercial samples of yogurt were obtained from retail stores in the local marketplace (Foggia, Italy). Because of the relatively high number of samples evaluated, it was impossible to obtain commercial samples that bore the same expiration (sell-by) dates. However, yogurt samples that exhibited the latest expiration dates possible were chosen from the store shelves. All containers, purchased as single-serving containers, were from the same lot. All yogurt samples were obtained no more than 3 days prior to the sensory evaluation.

The samples were labelled as follows: A, banana brand 1; B, banana brand 2; C, banana brand 3; D, banana brand 4; E, banana brand 5; F, banana brand 6; G, strawberry brand 3; H, strawberry brand 1; I, strawberry brand 5; L, strawberry brand 4; M, strawberry brand 2; N, strawberry brand 7; O, vanilla brand 5; P, vanilla brand 4; Q, vanilla brand 7; R, vanilla brand 3; S, plain yogurt brand 7; T, plain yogurt brand 1; U, plain yogurt brand 4; V, plain yogurt brand 2.

2.3.3. Descriptive and Consumer Panel

Sensory evaluation was conducted in the Science Laboratory at the Comprehensive Institute “Foscolo-Gabelli” (Foggia, Italy) by the pupils of group B through an internal protocol from the laboratory of Predictive Microbiology at the University of Foggia. The samples were placed on special counters consisting of separate stations, and spring water was provided for rinsing between samples. The serving temperatures was 3.3 °C, and the sample size consisted of 40 mL of yogurt served in 60 mL odourless plastic cups. Panellists rated all samples with two replications. Samples were presented in two sets, each consisting of either three or four samples.

Panellists rested between sets to avoid or minimize fatigue. They evaluated acidity, sweetness, odor, texture, taste, and overall acceptability using a 5-point scale, and answered two questions about their personal yogurt consumption frequency and whether they had ever bought the samples submitted for analysis.

2.3.4. Statistics

Data were analyzed using the Kruskal–Wallis test, chi square, and multiple comparison’s z-test, and graphically reported as box-whisker plots. In addition, multiple comparison among sensory scores (acidity, odor, taste, sweetness, texture, and overall acceptability) were performed. Statistical analysis was done through the software Statistica for Windows, ver. 10.0 (Statsoft, Tulsa, Okhla).

3. Results and Discussion

3.1. Sensory Scores

As a first step, sensory predictors were analyzed using non-parametric statistics as a function of brands; the scores were quite variable. Figure 1 shows the overall acceptability, revealing that brands S and U showed significantly lower acceptability than others, with both being plain yogurts. However, these lower sensory scores were not related to acidity, as these brands were not perceived as more acidic than the others. Thus, the leading hypothesis was that scores were affected by taste.

Therefore, in a second step, scores were analyzed using taste (banana, strawberry, vanilla, and plain yogurt) as predictors. Figure 2 shows the outputs for overall acceptability and taste. As expected, overall acceptability was strongly influenced by taste, as the yogurt with the highest scores were vanilla and strawberry-flavored ones, while plain yogurt samples were less preferred.

This result was influenced by taste, which followed the same trend.

3.2. Multiple Comparison

As the final step, data were analyzed through a multiple comparison procedure to assess if some sensory predictors affected the overall acceptability of yogurts, independent of taste. The outputs are shown in

Table 1. Multiple comparisons among predictors of sensory scores.

	Acidity	Sweetness	Odour	Taste	Texture	Overall Acceptability
Acidity	1.000	−0.564	−0.253	−0.475	−0.143	−0.517
Sweetness	−0.564	1.000	0.459	0.688	0.280	0.695
Odour	−0.253	0.459	1.000	0.591	0.391	0.587
Taste	−0.475	0.688	0.591	1.000	0.255	0.861
Texture	−0.143	0.280	0.391	0.255	1.000	0.345
Overall acceptability	−0.517	0.695	0.587	0.861	0.345	1.000

. The statistical analysis pointed out that for teenagers, overall acceptability was directly related to sweetness (0.695), odor (0.587), and taste (0.861), and indirectly related to acidity (−0.517), while negative correlations between taste and acidity (−0.564), and positive correlations between taste and sweetness (0.688) were perceived.

3.3. Reflection on STEM Approach

Finding teaching methods that capture pupils’ attention is certainly a challenge that schools face today. The goal is to guarantee significant learning for each student, anchoring new knowledge to existing ones and achieving educational success.

STEM teaching is continuously searching for innovative methodologies to achieve this goal and offer immediate answers to pupils who are at the center of the educational process. Transmitting content that requires increasingly advanced and specific skills for dealing with increasingly complex knowledge is complicated [17].

Bringing such young pupils closer to scientific research, for example, by making them experience the challenges that food microbiology and technology researchers face every day in the field, is the winning key to increase motivation and interest in this experimentation. This approach enabled students to possess discipline with a degree of maturity, surpassing that achieved through traditional study methods.

Furthermore, considering that the choice to participate in this course was free, pupils developed their own talents based on their personal aptitudes. This process significantly strengthened specific skills and competences, leading to them acquiring a higher degree of knowledge than typically required at their school grade. In addition to obtaining positive results in the possession of knowledge and skills, this approach was fundamental in structuring critical thinking, in turn, favoring a more conscious orientation towards future study courses and professional choices.

All of this has favored an increase in well-being at school, confirming that working on students’ talents and natural predispositions through innovative educational paths that stimulate their interest is the winning key to developing happiness as a life skill at school [17].

4. Conclusions

This research offers an important contribution to elucidating the perspectives of adolescents, providing significant contributions for studies on consumer knowledge within the functional food market. Furthermore, it provides an innovative approach to the fields of pedagogy and orientation teaching, by bringing young pupils closer to scientific research from an early age, strengthening specific skills with the aim to more effectively structure of process of pedagogical orientation, guiding students towards increasingly aware future choices.

From a technical perspective, the results show that pupils’ overall acceptability of yogurt is positively affected by sweetness, odor, and taste, and negatively affected by acidity.