Optimasi serta Validasi Metode Analisis untuk Penetapan Kadar Protein, Asam Lemak, dan Serat dalam Ekstrak Ragi Hasil Fermentasi Saccharomyces cerevisiae = Optimization and Validation of Analytical Methods for Determination of Protein, Fatty Acid, and Fiber Levels in Yeast Extract from Fermentation of Saccharomyces cerevisiae