The fast-growing e-reader market is finding its way into the American kitchen. Austin,Texas-based Key Ingredient is betting that the explosion of low-cost e-readers will make information about preparing food an underserved content niche. The firm, a veteran of the online publishing wars, has been offering Web-based cooking tips, recipes and blogs for about five years. The site is a mix of home cooking tips, social content, blogs and professional advice about food prep and the culinary life. The mainstream cooking elite have taken notice. Martha Stewart and Oprah have reviewed and recommended the product on their respective media outlets.