Research Article Received: 12 September 2019 Revised: 13 April 2020 Accepted article published: 23 April 2020 Published online in Wiley Online Library: 19 May 2020 (wileyonlinelibrary.com) DOI 10.1002/jsfa.10429 Raw and roasted pistachio nuts (Pistacia vera L.) are ‘good’ sources of protein based on their digestible indispensable amino acid score as determined in pigs Hannah M Bailey and Hans H Stein* Abstract BACKGROUND: Pistachio nuts may be consumed as raw nuts or as roasted nuts. However, there is limited information about the protein quality of the nuts, and amino acid (AA) digestibility and protein quality have not been reported. Therefore, the objec- tive of this research was to test the hypothesis that raw and roasted pistachio nuts have a digestible indispensable AA score (DIAAS) and a protein digestibility corrected AA score (PDCAAS) greater than 75, thereby qualifying them as a good source of protein. RESULTS: The standardized ileal digestibility (SID) of all indispensable AAs, except arginine and phenylalanine, was less in roasted pistachio nuts than in raw pistachio nuts (P < 0.05). Raw pistachio nuts had a PDCAAS of 73, and roasted pistachio nuts had a PDCAAS of 81, calculated for children 2–5 years, and the limiting AA in the PDCAAS calculation was threonine. The DIAAS values calculated for children older than 3 years, adolescents, and adults was 86 and 83 for raw and roasted pistachio nuts respectively. The limiting AA in both raw and roasted pistachio nuts that determined the DIAAS for this age group was lysine. CONCLUSION: The results of this research illustrate that raw and roasted pistachio nuts can be considered a good quality pro- tein source with DIAAS greater than 75; however, processing conditions associated with roasting may decrease the digestibility of AAs in pistachio nuts. © 2020 Society of Chemical Industry Keywords: protein digestibility corrected amino acid score; digestible indispensable amino acid score; pistachio nuts; pig model vitamin B1, vitamin B6, vitamin K, and potassium, magnesium, cal- INTRODUCTION 5,6 fi cium, and copper. Pistachio nuts (Pistacia vera L.) have been identi ed in archeologi- −1 cal excavations indicating that they have been associated with Pistachio nuts, at the time of harvest, contain 400 to 500 g kg 1 moisture on a fresh weight basis and must be dried to about human activity for centuries. Pistachio nuts are thought to be −1 2 50 g kg moisture to inhibit fungal growth, prevent rancidity, originally native to Iran, Afghanistan, and central Asia, but they 8,9 are currently being cultivated and grown in a variety of climates.1 improve sensory characteristics, and extend shelf life. Pistachio Iran, the USA (only California), and Turkey are the top three pro- nuts can be consumed in raw or roasted forms. Several health fi ducers of pistachio nuts, and in 2018 these countries produced bene ts in relation to metabolic conditions and cardiovascular approximately 551 000 t, 448 000 t, and 240 000 t of pistachio health have been associated with the bioactive compounds and 6,10 nuts respectively.3 lipid composition of pistachio nuts. However, to our knowl- The majority of edible nuts (e.g. pistachios, cashews, chestnuts, edge the quality of protein in pistachio nuts and the effect of pecans, brazil nuts, peanuts, macadamia nuts) are rich sources of roasting on protein quality have not been studied. Therefore, lipids, protein, and minerals.2,4 Lipids make up a significant por- the objective of this work was to determine the ileal digestibility tion of the composition of edible nuts, ranging from approxi- of amino acids (AAs) in raw and roasted pistachio nuts and to test mately 450 to 700 g kg−1,2,4,5 but pistachio nuts have among the hypothesis that the protein digestibility corrected AA score the least concentration of lipids, at approximately 450 g kg−1.6 (PDCAAS) and the digestible indispensable AA score (DIAAS) in The concentration of protein in edible nuts ranges from approxi- both raw and roasted pistachio nuts are greater than 75. mately 75 to 220 g kg−1 if a nitrogen-to-protein conversion factor of 5.3 is used,7 and pistachio nuts have a greater protein concen- * tration (approximately 210 g kg−1) than most other nuts.6 In addi- Correspondence to: HH Stein, Division of Nutritional Sciences, University of tion, mineral concentrations in edible nuts range from Illinois, 1207 West Gregory Drive, Urbana, IL 61801, USA. E-mail: [email protected] 3878 approximately 10 to 35 g kg−14(approximately 32 g kg−1 in pis- tachio nuts6), and pistachio nuts are rich in vitamin A, vitamin E, Division of Nutritional Sciences, University of Illinois, Urbana, IL, USA J Sci Food Agric 2020; 100: 3878–3885 www.soci.org © 2020 Society of Chemical Industry PDCAAS and DIAAS for pistachio nuts www.soci.org MATERIALS AND METHODS first experimental period, animals were deprived of feed over- The protocol for the experiments in this study was reviewed and night, and the following morning the new experimental diet approved by the Institutional Animal Care and Use Committee was offered. at the University of Illinois. Two protein sources, raw pistachio nuts and roasted pistachio nuts, were used in this study Chemical analysis (Table 1). Pistachio nuts were roasted in a commercial rotary batch At the end of the experiment, fecal samples were dried and roaster. Roasters were preheated to 176 °C. Once nuts were ground through a 1 mm screen in a Wiley Mill (model 4; Thomas added, nut temperature was gradually increased to 115 °C. They Scientific, Swedesboro, NJ, USA) prior to chemical analysis. Ileal were then removed from the roaster and allowed to cool to room digesta samples were thawed, mixed within animal and diet, temperature. The entire roasting process took approximately and a subsample was collected for chemical analysis. Ileal digesta 30 min. Raw and roasted pistachio nuts were ground using a roller samples were lyophilized and finely ground prior to chemical mill prior to addition to the diets. analysis. Samples of all ingredients, diets, fecal samples, and ileal digesta samples were analyzed for dry matter (Method 927.05)7 and for nitrogen by combustion (Method 990.03)7 using a Leco Diets, animals, and feeding FP628 analyzer (Leco Corp., Saint Joseph, MI, USA). A nitrogen- Three diets were prepared (Tables 2 and 3) with the two pistachio to-protein conversion factor of 6.25 was used to calculate CP as proteins included in one diet each as the only AA-containing recommended by the Food and Agriculture Organization of the ingredient. A nitrogen-free diet was also formulated and used to United Nations (FAO) for the calculation of PDCAAS and measure basal endogenous losses of AAs and crude protein DIAAS.13,14 All diets, fecal samples, and ileal digesta samples were (CP). Vitamins and minerals were included in all diets to meet or also analyzed for titanium (Method 990.08),15 and all diets, ingre- exceed current nutrient requirement estimates for growing dients, and ileal digesta samples were analyzed for AAs (Method pigs.11 Diets also contained 4 g kg−1 titanium dioxide as an indi- 982.30 E (a, b, c)).7 gestible marker, and all diets were provided in meal form. Sam- ples of each pistachio protein and of all diets were collected at Calculations the time of diet mixing and used for chemical analysis. Values for apparent ileal digestibility (AID), basal endogenous Twelve growing barrows (initial body weight 60.9 ± 3.2 kg) losses, and standardized ileal digestibility (SID) of CP and AAs in were equipped with a T-cannula in the distal ileum.12 Following each diet were calculated based on equations from Stein et al.16 surgery, pigs were randomly allotted to a two-period switch-back The standardized total tract digestibility (STTD) of CP was also design with three diets and four replicate pigs in each period; calculated.17 therefore, there were eight replicate pigs per treatment. Each Values for the STTD of CP were used to calculate PDCAAS using period was 9 days; therefore, the entire experiment lasted the following equation:13 MassðÞ mg of limiting AA in 1 g of test protein PDCAASðÞ % = ×100 ð1Þ MassðÞ mg of the same AA in 1 g of reference protein×Standardized total tract digestibilityðÞ % 18 days. Pigs were housed in individual pens (1.2 m × 1.5 m) in The calculation of PDCAAS was accomplished using the refer- an environmentally controlled room. Each pen had smooth sides ence protein pattern for preschool children from 2 to 5 years of and fully slatted tribar floors. A feeder and a nipple drinker were age.13 Values were calculated using a nitrogen-to-protein conver- installed in each pen. sion factor of 6.25,13 as well as a conversion factor of 5.3.7,18 All pigs were fed their assigned diets in a daily amount equiva- Values for the SID of AAs were used to calculate DIAAS reference lent to 40 g kg−1 of the body weight for each pig. Two equal ratios for each AA using the following equation:19 meals were provided daily at 08:00 and 16:00, and water was avail- Digestible IAA reference ratio able at all times. Pig weights were recorded at the beginning of ðÞ each period and at the conclusion of the experiment. The amount = Digestible IAA content in 1 g protein of food mg of feed supplied each day was also recorded. MassðÞ mg of the same dietary IAA in 1 g of the reference protein ð2Þ Sample collection where IAA is the indispensable AA. Experimental periods were 9 days, with the initial 5 days being The DIAAS was calculated for children older than 3 years, ado- the adaptation period to the diet.