At present, we face a worldwide crisis of global warming, a consequence of the way we have utilised our resources on earth for the last centuries. Food production and consumption are recognised as major contributors to the global warming crisis and are consequently included in the UN sustainable development goals for 2030, thus being an important part of solving the global climate challenge. Investigations into new sustainable sources of food and investigations of palatability of future sustainable foods can both help facilitate the needed change in our food system in the future.
It is increasingly agreed upon that meat from terrestrial animals is generally burdensome for the environment. Consequently, an increasing trend in some Western countries, driven by the motivation of eating more sustainable, is to cut out meat and eat a plant-based diet, i.e. eating a vegetarian or vegan diet. However, a strictly plant-based diet can pose some challenges of both nutritious and taste-wise nature. Possible approaches to meet these challenges are therefore presented in the present PhD thesis, namely eating a predominantly plant-based diet using only little animal-based meat from sustainable sources, securing both delicious taste and nutritive dietary content. Another, or additional, approach presented is how to pair foods and foods and beverages to gain umami taste synergy, which can also be used to compose a delicious strictly
plant-based sustainable meal.
The present PhD thesis investigates future possible sustainable sources of animal-based protein from currently unexploited marine resources. In Scandinavia, and Denmark in particular, such examples are macro- and microalgae, scrap fish, invasive oysters and cephalopods. The present thesis investigated the umami taste potential of invasive oysters (Crassostrea gigas) and abundant unexploited squid (Loligo forbesii and L. vulgaris) present in the North Sea and North Atlantic Ocean, of which squid was also investigated to optimise its textural eating quality. It is shown that squid possesses a complex protein structure inside the flesh of the mantle, ascribed to the biology of squid muscle being a muscular hydrostat. The collagen content in the common cuts of Nordic squid was quantified and found to be greatest in arms (4.3 % of total protein), then fins (3.0 %) and lowest in the mantle (1.5 %), which for mantle is rather low compared to other species of squid. Collagen and in specific the structural nature and arrangement of the protein structure in the mantle will challenge the final eating quality and consequently sets certain requirements to the cooking technique applied. Physicochemical investigation by differential scanning calorimetry (DSC), compared to various gastrophysical methods of texture analysis (TA), small-angle x-ray scattering (SAXS), second-harmonic generation microscopy (SHGM), and Raman spectroscopy (RS), additionally compared to chemical analysis of amino acids by ultra-high performance liquid chromatography (UHPLC) and 5’-ribonucleotides by high-performance liquid chromatography (HPLC), were applied to investigate structural changes affecting cooking loss and perceived texture. Structural changes related to cooking loss were related to collagen while structural changes related to mechanical texture were ascribed to collagen and actin. Further, an optimal eating outcome was found to be attainable by applying certain sous vide cooking treatments. In specific, a significant decrease of cooking loss was obtained using a lower cooking temperature, while maintaining somewhat similar mechanical textural characteristics, by using a cooking temperature of 55 °C instead of 77 °C. These findings were furthermore compared to sensory evaluation of selected sensory properties and hedonic responses, which concluded that Danish consumers (n=
129) prefer squid to be well done over rare. Additionally, the results suggest that there may be a market for squid in Denmark, indicated by the fact that Danish consumers rated squid well above neutral. Furthermore, the umami taste potential of Nordic squid was found to be substantial. In particular the liver, which is generally discarded, was found to contain the highest amount of umami-specific compounds (equivalent umami concentration, EUC= 2.3×104 mg/100 g) followed by cooked mantle (EUC = 3.5×103 mg/100 g) > raw mantle (EUC = 3.3x103 mg/100g) > fins (EUC = 2.3×103 mg/100 g) > arms (EUC = 1.7×103 mg/100 g), with all values referring to fresh weight. Also, invasive oysters were found to possess an abundant umami potential (Glu= 160 mg/100g, guanosine monophosphate= 9 mg/100g, inosine monophosphate= 15 mg/100g, adenosine monophosphate= 42 mg/100g), however significantly lower than that found in native European flat oysters, but still well above the umami taste threshold (30 mg/100g).
Umami taste characterisation was further investigated as a mean of obtaining delicious taste in food-beverage pairing, which can just as well be applied in food pairing. A strictly plant-based diet may lack umami taste that is characteristic of meat and animal-derived foods. This is a problem if we want to make the majority of the global population change their consumption habits and
adhering to it. Umami taste is well-liked across food cultures, gender and age and can therefore be considered as a universal phenomenon. The basal umami taste is facilitated by the presence of free glutamate (Glu) which is the salt of the amino acid glutamic acid, acting by an allosteric action on the T1R1/T1R3 taste receptor. The simultaneous presence of the salts from certain free 5’- ribonucleotides is well recognized to elicit a synergistic umami taste effect, facilitated by a wellknown molecular mechanism on the Venus-flytrap motif of the umami taste receptor. An immense perceived taste effect can thereby be created by only small contributions of either of two types of umami taste compounds. Plant-based diets are in general low in Glu and particular lack 5’- ribonucleotides, thus challenging the ability to obtain strictly plant-based meals being high in perceived umami taste. Knowledge derived from the present PhD thesis can therefore be applied to obtain palatable sustainable plant-based diets. To underline the practical application that possible lies behind this scientifically well-established principle of umami synergy, the present PhD project, therefore, investigated whether umami synergy can explain good food-beverage pairings, with the case study of champagne paired with oysters. Based on quantitative chemical measurement of umami taste compounds in a great variety of champagnes and two different species of oysters (Crassostrea gigas and Ostrea edulis) it was suggested that a reason why champagne and oysters are considered such good companions is the presence of respectively free Glu in champagne, and Glu and free 5’-ribonucleotides in oysters. By calculations of the effective umami potential of different combinations, it could further be revealed which combinations of oysters and champagnes that lead to the strongest umami taste. The umami taste compounds of other categories of fermented beverages (wine, sake, and beer) were additionally investigated concerning their theoretical pairing potential to selected foods, to uncover their respective effective umami taste potential, and additionally, whether long yeast contact and ageing can influence the contents of free Glu in beverages. The data showed that in particular sakes, but also some beers, wines and champagnes with long yeast contact, contain appreciable amounts of free Glu. These results may point to fermentation, in particular by koji, as a promising technique to obtain umami taste in a meal, which can as well be regarded as a promising future preparation technique for processing plant-based foods and not just beverages.
The present PhD project applied a comprehensive, state of the art combination of different methods investigating the structural proteins in squid mantle and their behaviour upon sous vide cooking. The methods applied have not previously been used all at once investigating the same sample. Furthermore, the project investigated new application possibilities of umami taste pairing that can be put to direct use by the general public, chefs and food professionals, based on a scientifically sound phenomenon of allosteric taste-enhancing on the Venus flytrap of the umami taste receptor. This project uncovered squid and invasive oysters as future sources of food for Danish and possibly also other Scandinavian consumers, suggesting that these sources can play a role in sustainable eating. All included research was discussed in specific with regards to supporting a sustainable transition of the food production as well as consumption. This work underlines that sustainability is not a one-way street, meaning that one solution does not fit all. The PhD project consequently provides a framework that applies to consumers who are willing to change their diets to be vegetarian or vegan, but as well to those that are not. In specific, a possible solution of how to meet the current global environmental challenge by looking into unexploited sources of food, as well as providing a framework for making future sustainable plant-based diets taste better, is presented by this PhD project.