Food Biochemistry and Food Processing

2

Analytical Techniques in Food

Biochemistry

M. Marcone

25

Introduction
Protein Analysis
Lipid Analysis
Carbohydrate Analysis
Mineral Analysis
Vitamin Analysis
Pigment Analysis
References

INTRODUCTION

Without question, food can be considered as a very
complex and heterogeneous composition of hun-
dreds, if not thousands, of different biochemical
compounds. In the area of food biochemistry, the
isolation and quantitative measurement of these
chemical components has posed, and continues to
pose, immense challenges to the analytical bio-
chemist. Without the ability to measure both specifi-
cally and quantitatively those biochemical compo-
nents in food matrices, further advancements in the
understanding of how foods change during matura-
tion or processing would not be possible.
Although it is impossible to address the quantita-
tive analysis of all the different food components, the
major techniques for the analysis of protein, lipids,
carbohydrates, minerals, vitamins, and pigments
will be addressed in detail in this chapter. The prin-
ciples behind their analysis are the building blocks
for other analytical determinations, including tech-
niques such as gas chromatography, high perform-
ance liquid chromatography (HPLC), and spectros-
copy, including infrared and mass spectroscopy.

PROTEIN ANALYSIS

Proteins are considered to be among the most abun-

dant cell components and, except for storage pro-

teins, are important for biological functions within

the organism—plant or animal. Many food proteins

have been purified and characterized over the years

and found to range from approximately 5000 to

more than a million Daltons. In general, they are all

composed of various elements including carbon,

hydrogen, nitrogen, oxygen, and sulfur. These ele-

ments are formed into twenty different amino acids,

which are linked together by peptide bonds to form

proteins. In general, nitrogen is the most distin-

guishing element in proteins, varying from approxi-

mately 13 to 19% due to variations in the specific

amino acid composition of proteins (Chang 1998).

For the past several decades, protein analysis has

been performed by determining the nitrogen content

of the food product after complete acidic hydrolysis

and digestion by the Kjeldahl method and subse-

quent conversion to protein content using various

conversion factors (Chang 1998, Diercky and Huy-

ghebaert 2000). As far back as the turn of the centu-

ry, colorimetric protein determination methods such

as the Biuret procedure (which exploited the devel-

opment of the violet-purplish color that is produced

when cupric ions complex with peptide bonds under

alkaline conditions) became available. The color ab-

sorbance is measured at 540 nm, with the color in-

tensity (absorbance) being proportional to the pro-

tein content (Chang 1998) with a sensitivity of 1–10

mg protein/mL. Over the years, further modifications

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing