Increased value creation of Norwegian Brassica vegetables - mapping sensory quality and plant compounds to improve consumer choice

Cabbage plants in the species Brassica oleracea are important and traditional vegetables in the Nordic diet and excellent sources for essential nutrients and health-promoting phytochemicals. Although sales of vegetables in Norway have increased lately, Brassicas did not see the same rise. The key factor for value creation within the cabbage segment could be product differentiation, such as for tomato and potato. The bitter and sulfurous taste and the consumers? lack of knowledge on taste and usage of different cultivars, is often a hindrance. Today there is little research-based knowledge about how sensory properties (taste, smell and texture), content of taste- and health-related plant compounds and crop characteristics vary and interact in different cabbage cultivars produced in Norway. Thus, is it true that taste-intensive cabbages have higher content of healthy plant compounds than milder ones? How does the taste and health value of cabbage growth affect cultivation conditions? The main goal was to establish and disseminate knowledge about sensory characteristics in selected cabbages, their content of taste-, smell- and health-related plant compounds, and the relationship between these parameters. Several different cultivar trials have been performed in fields hosted by local producers: a total of 27 different cultivars of head cabbage, both well-established and new cultivars (round, flat, pointy, white or red) were grown in summer, autumn or winter season; in addition, 11 cultivars of cauliflower and 12 cultivars of leafy cabbage, were grown. Crop growth-related traits were evaluated during cultivation, and a professional sensory panel performed descriptive analysis of sensory attributes on fresh products shortly after harvest. There were distinct differences between cultivars of head cabbage within each season, and there were both sweet/mild and taste-intensive round and pointy cultivars, which constitutes a good basis for product differentiation within the head cabbage segment. Even larger differences were found between cultivars of leafy cabbage, with some clear differences in sensory characteristics. Cauliflower cultivars were much more similar in their sensory attributes, especially in their taste, but some cultivars were different in texture and smell. Sensory descriptive maps (Taste-maps) were created based on principal component analysis (PCA) that visualize cultivars and the sensory characteristics that were the most descriptive for the cultivars in each season. These 'maps' are useful when selecting a cultivar for different use, e.g. for fresh consumption or industrial processing based on texture, color and taste. Phytochemicals with relevance for taste, aroma and health, like volatile compounds, sugars, glucosinolates, vitamin C and water content were determined for all cultivars. The head cabbage and leafy cabbage cultivars varied more in their content of plant compounds than the cauliflower cultivars. High intensity of sulfurous and pungent taste and aftertaste often characterized the cultivars which also had high levels of glucosinolates, health-related compounds, but not always. This is important information regarding choice of cultivars for the market. Volatile aroma compounds that distinguish cultivars were analyzed and identified by metabolomics methodology. PCA and PLS plots (Aroma maps) provided visual correlations between groups of volatiles and sensory characteristics of the cultivars. Aftertaste and astringency increased with increasing content of isothiocyanates (ITCs) and aldehydes. In experiments where exhaled air from people was analyzed via Proton-transfer-reaction mass spectrometry during chewing of cabbage, it became clear that single ITCs and aldehydes have a longer dwelling time in the oronasal cavity than others and thus affect aftertaste. During 2 years, the project has documented how nitrogen and sulfur fertilization (3 by 3 levels) affect head cabbage and cauliflower quality traits, and how drought stress (3 levels) during production affects cauliflower quality traits. For head cabbage, there was an effect of N-level on plant size and plant vigour in both years, but there was little effect of different sulfur levels. In cauliflower, there was almost no effect of N- and S-level on the crop-related traits. N- and S-levels had little effect on the taste and smell of cabbage and cauliflower, while texture was influenced by N-level both years. The content of aroma- and health-related phytochemicals was influenced by N- and S-levels, both in cabbage and cauliflower. Drought stress did not significantly affect crop-related properties but caused less sweetness and crispness and led to an increase in glucosinolates and flavor-intense aroma compounds (ITC and nitriles). Our results show that supply and management of nitrogen, sulfur and water during growth can affect sensory- and health-related quality without necessarily affecting the visible quality of cabbages.

Prosjektet KålSmak har gitt ny, tverrfaglig kunnskap om dyrkingsrelaterte, sensoriske (smak, lukt, tekstur)- og helserelaterte egenskaper til nye og etablerte sorter av hodekål, blomkål og ulike typer bladkål under norske vekstvilkår. Kunnskapen vil bidra til økt produktdifferensiering innen kålvekster, slik at både matindustri og forbruker enklere kan velge «rett sort til rett bruk». Prosjektet har etablert en database med de nevnte egenskaper for 50 ulike sorter hodekål, blomkål og bladkål. Resultatene skal bidra til å gjøre mer bevisste sortsvalg fremover basert på samlet kunnskap om sortenes dyrkingspotensiale, vekstegenskaper, sensoriske egenskaper, helseverdi og bruksmuligheter. Det er også av betydning for hele verdikjeden å ha kunnskap om at tilgang på nitrogen, svovel og vann under vekst kan påvirke sensorisk og helsemessig kvalitet uten nødvendigvis å påvirke synlig kvalitet av kålvekster.

Increased vegetable consumption is a goal in the nutritional guidelines issued by the Norwegian health authorities. Brassica vegetables, also known as cabbages, are important parts of a Nordic diet and excellent sources of essential nutrients and a range of health-promoting phytochemicals. However, the bitter and sulphurous taste and variable sensory quality of these vegetables are often hinders for consumers to increase their Brassica consumption. To date little is known about how sensory attributes vary among Brassica varieties and their cultivars, or how they are affected by climate and crop production factors. Hence, delivering Brassica vegetables with a stable sensory quality and distributing knowledge about their sensory attributes to the consumer is challenging for both growers and traders. In the present project, the aim is to generate and disseminate knowledge about the sensory attributes of Brassica vegetables, their content of taste-, flavour- and health-associated plant compounds and the relationship between these parameters. The work will include generation of sensory descriptive maps as well as mapping of the content and chemical variation of plant compounds in cauliflower, white cabbage and leafy cabbage in different seasons, and Brassica grown under varied nutrient (N and S) regimes. Improved knowledge on how genetic and environmental factors influence the sensory and nutritional quality will give Brassica producers a potential tool to impact the quality already during the growing season. It will also provide traders a potential for product differentiation, and give consumers information about the expected sensory attributes of Brassica products. This project will create a much needed knowledge base for the participating companies and the producers of Brassica vegetables.