Why did we start Fermenting cereals? A molecular dissection of Ancient Bread and Beer making (FABB)

点击翻译按钮获取中文摘要

Cereals have formed part of the human diet for more than 20,000 years, though fermented cereal products such as beer and leavened bread are more recent innovations. Although the use of fermentation to preserve and to improve the digestibility and nutritional value of foods likely pre-dates the Neolithic by several tens of thousands of years, the fermentation of cereals is thought to have been established between 6,000 and 3,500 years ago in ancient Egypt, where bread baking was closely associated with beer brewing. There is considerable interest in understanding the early innovations in cereal fermentation that laid the foundations for the breads and beers we know today. A central question is the nature of the microorganisms (yeast and bacteria) used in the fermentation of these early leavened breads and beer. While the earliest beer and bread may have depended on wild yeasts present on the surface of fruits that were added to impart flavour, an alternative possibility is the use of spontaneous sourdough cultures, a stable mix of wild yeasts and lactic acid bacteria (LAB) present on cereal grain. Importantly, sourdough fermentation offers advantages over 'pure' yeast fermentation in the complete breakdown of phytate, an anti-nutrient present in cereal grains which contributes to several mineral deficiencies. We hypothesise that fermentation of cereals became established in ancient Egypt because it offered nutritional advantages in the breakdown of cereal phytate at a time when cereals made up the bulk of the diet. In this project we will use ancient DNA (aDNA) sequencing and metagenomic analysis of ancient Egyptian bread and beer samples, to provide the most comprehensive analysis to date of the ingredients of ancient bread and beer. Importantly, we will identify the yeast(s) and LABs in these breads and beers, and determine whether ancient Egyptian breads (and beer) were made with sourdough cultures, or with yeast only. We will also use state-of-the-art biomolecular analysis to measure phytate levels in these ancient bread and beer samples, to test our hypothesis that fermentation reduced phytate levels and increased the nutritional value of cereal foods. We will use experimental archaeology to investigate the ancient Egyptian baking process, based on our metagenomic analysis, and finally, we will also attempt to isolate live yeasts from ancient Egyptian beer samples.