The Effect of Plant Food Treatment on Stable Isotopes and Their Relevance for Archaeological Studies: A Methodological Pilot Study

Abstract

Plants are a crucial part of the human diet, serving as a primary source of micronutrients, fiber, and carbohydrates, providing readily available energy. Beyond the consumption of cooked and raw edible plants, early humans also developed methods for plant processing for delayed consumption, to de-toxify/improve bioavailability, and perhaps for flavor. In later prehistory delayed consumption includes preservation processes for storage. The processing of plants through sprouting, fermentation, cooking, and roasting has not only expanded the variety of consumable plant species but also enhanced their nutritional value. There are few methods for detecting fermented foods in the early prehistoric diet. Based on the hypothesis that the microbes active in fermentation change the nitrogen and carbon isotope ratios of plant foods, our pilot study lays the groundwork for further research, offering a promising direction for understanding the complexities of human-plant interactions throughout history. This study focuses on these four plant treatment methods, which have both contemporary relevance and archaeobotanical evidence of use. We aimed to explore how these treatments might affect stable isotope values, such as carbon (δ¹³C) and nitrogen (δ¹⁵N), which are crucial for reconstructing ancient diets. Through an experimental approach involving 12 plant species, our findings suggest that while sprouting and roasting had minimal impact on isotopic values, fermentation and cooking showed more variable effects depending on the plant species. These preliminary results provide new insights into the influence of plant processing on isotopic compositions and underscore the importance of considering these factors in dietary reconstructions.