Hello, my name is Hannah Bailey, and I am a Ph. D. student working under Dr. Hans Stein at
the University of Illinois. Our lab focuses on determining values for digestibility of
energy and nutrients, and in recent years we have been conducting research to determine
digestible indispensable amino acid scores (abbreviated DIAAS) for a variety of human
foods. We specifically conducted this experiment to determine the protein digestibility
corrected amino acid score (abbreviated PDCAAS) and the DIAAS for raw and roasted
pistachio nuts in growing pigs. The second objective of this experiment was to assess the
effect of roasting on these measurements of protein quality.

The DIAAS and PDCAAS methodologies were developed by the Food and Agriculture Organization
in 1989 and 2011, respectively. DIAAS has been the approved successor to PDCAAS for
measuring protein quality; however, until more research is conducted to determine DIAAS
for human foods, PDCAAS will be used.

Pistachio nuts are edible nuts thought to be originally native to Iran, Afghanistan, and
central Asia. Pistachio nuts can be consumed in raw or roasted form, and compared with
other nuts, pistachios have among the least lipid and greatest protein concentration.
However, heat processing can affect amino acid bioavailability and therefore protein
quality. To our knowledge the quality of protein and the effect of roasting on protein
quality of pistachio nuts have not been studied.
      
Two forms of pistachio nuts were evaluated: raw and roasted. The pistachio nuts were
roasted to a temperature of 115 oC, which took approximately 30 minutes. For this
experiment, 12 ileal cannulated barrows with an initial body weight of 60.9 kg were used.
The experimental design was a 2-period switch-back design with 3 diets using each
ingredient as the sole source of protein and amino acids plus a nitrogen-free diet to
determine basal endogenous losses of protein and amino acids. There were 2 periods, and
each period was 9 days with fecal collection on day 6 and 7 and ileal digesta collection
on day 8 and 9. A nitrogen-to-protein conversion factor of 6.25 was used in all protein
calculations. PDCAAS and DIAAS were calculated at the conclusion of the experiment for
preschool children 2 to 5 years of age and for children older than 3 years, adolescents,
and adults, respectively.
      
Moving to the results, the crude protein content was greater in raw pistachio nuts, 27.1%,
compared with roasted pistachio nuts, 25.1%, using a nitrogen-to-protein conversion factor
of 6.25 as mentioned earlier. The results for standardized ileal digestibility, or SID, of
some indispensable amino acids are shown in the top bar graph on the right of this slide.
The orange bar represents raw pistachio nuts and the blue bar represents roasted pistachio
nuts. These colors also match the bottom bar graph on the right showing the PDCAAS and
DIAAS results. The SID of protein and all indispensable amino acids (except arginine and
phenylalanine, not shown on this slide) was greater in raw than in roasted pistachio nuts.
For PDCAAS and DIAAS shown on the bottom right bar graph, the first limiting amino acid,
which determines the PDCAAS and DIAAS value, for both raw and roasted pistachio nuts when
compared with the human amino acid requirements for the specific age group was threonine
for PDCAAS and lysine for DIAAS. The PDCAAS for roasted pistachio nuts was 81, which was
greater than the PDCAAS for raw pistachio nuts, 73. In contrast, the DIAAS for roasted
pistachio nuts was 83 and less than the DIAAS for raw pistachio nuts which was 86. This
illustrates that DIAAS, which is determined via standardized ileal digestibility, more
accurately determines the bioavailability of heat damaged amino acids compared with
PDCAAS, which is determined via standardized fecal digestibility.

In conclusion, raw and roasted pistachio nuts can be considered good quality protein
sources with DIAAS greater than 75 for children older than 3 years, adolescents, and
adults. However, roasting pistachio nuts may decrease ileal digestibility of amino acids
and DIAAS, whereas PDCAAS was not reduced. Therefore, PDCAAS is unable to account for
decreased amino acid digestibility due to heat damage from roasting nuts.