坚果中蛋白质检测方案(电热消解仪)

APPLICATION NOTEF&F-K-002-2015/A1 N/PROTEIN DETERMINATION IN NUTSKJELDAHLMETHOD N/Protein Determination in Nutsaccording to the Kjeldahl method Reference： AOAC 950.48 Protein (Crude) in Nuts and Nut Products Tested with VELP Scientifica DKL 20 Automatic Kjeldahl Digestion Unit (Code S30100210) andUDK 169 Automatic Kjeldahl Analyzer with AutoKjel Autosampler (Code S30200160). Introduction Recently there was an archeological dig in Israel where researchers found evidence showing that nuts formed a major part of man's diet 780，000 years ago. Seven varieties of nuts along with stone tools to crack open the nuts were foundburied deep in a bog. Even then man was aware of the health benefits connected to the consumption of nuts. In fact nutsare an excellent source of protein and healthy fats； the amounts vary depending on the type of nut.Peanuts provide a good source of B vitamins essential for energy， protein metabolism， and the synthesis of red bloodcells. Their protein content is about 29 %. Peanuts can be eaten raw， dry roasted and salted. Popular confections madefrom peanuts include salted peanuts， peanut butter (sandwiches， peanut candy bars， peanut butter cookies， and cups)，peanut brittle， and shelled nuts (plain/roasted). Almonds contain about 20 % of protein. Almonds are often eaten on theirown， either raw or toasted， and are also a component of various dishes. Almonds are available in many forms， such aswhole， flaked， slivered and ground. Almonds yield almond oil and can also be made into almond butter or almond milk.These products can be used in both sweet and savoury dishes. Nitrogen Determination in Nuts according to the Kjeldahl Method Thanks to the high level of precision and reproducibility and to its simple application， Kjeldahl is nowadays the most usedmethod for determining nitrogen and protein contents in the food and feed industry. It also has several other applicationsin environmental control (phenols and nitrogen in water， sludge， soil and lubricants) and in the chemical andpharmaceutical industry according to official AOAC， EPA， DIN e ISO procedures. The modern Kjeldahl method consists in a procedure of catalytically supported mineralization of organic material in aboiling mixture of sulfuric acid and sulfate salt at digestion temperature higher than 400℃. During the process theorganically bonded nitrogen is converted into ammonium sulfate. Alkalizing the digested solution liberates ammonia whichis quantitatively steam distilled and determined by titration. Samples Raw almonds Expected Protein range： 15-25%Raw peanuts Expected Protein range：20-30 % Sample Digestion Samples have been freeze and quickly homogenized by grinding， in order to avoid loss of oil (particle size 0.5 mm).Weigh about 0.500 g of sample into a nitrogen-free weighing boat (code CM0486000) and place it into a 250 ml test tube.For each sample， add in the test tube： ● 2 catalyst tablets Kjtabs VCM (code A00000274；3.5 g K2SO4， 0.1 g CuSO4*5H20 Missouri) 2 antifoam tablets VS (code A00000283) ● 20 ml concentrate sulphuric acid (96-98%) ● 5 ml hydrogen peroxide (30-32%) Prepare some blanks with all chemicals and without the sample Connect the Digestion Unit to a proper Aspiration Pump (JP code F30620198) and a Fume Neutralization System(SMS Scrubber code F307C0199) to neutralize the acid fumes created during digestion phase.Digest the samples for 30 minutes at 300°C and 60 minutes at 420 °C， according to the method “almonds， nuts， hazelnuts”or“peanuts and Brazil nuts” (respectively n° 2 and 4 on DKL 20). Distillation and Titration Let the test tubes cool down to 50-60 C. Condition the UDK 169 with AutoKjel Autosampler unit by performing theAutomatic Check-up and Wash-down in the Menu-System. Distill the samples according to the following parameters (pre-defined method n°2 for almond and n°4 for peanuts)： ●HH2O (dilution water)： 50 ml NaOH (32%)： 70 ml. HH2SO4 (0.1 N) as titrant solution H3BO3 (4 % with indicators)： 30 ml. PProtein factor： 5.18 for almonds and 5.46 for peanuts Distillation & Titration analysis time： from 4 minutes for one test. VELP Scientifica， Italy Tel： +39039 628 811 Fax： +39 039 6288120 www.velp.com Typical Results on Nuts Sample Sample quantity (g) Nitrogen% Protein% Raw almonds 0.496 3.807 19.718 0.500 3.785 19.604 0.499 3.816 19.769 0.502 3.829 19.834 0.502 3.817 19.774 0.500 3.826 19.718 Average± SD% 3.813±0.016 19.753±0.084 RSD%* 0.418 0.425 Raw peanuts 0.500 4.196 22.910 0.502 4.144 22.626 0.502 4.212 22.998 0.505 4.189 22.872 0.508 4.131 22.555 0.509 4.172 22.779 Average ±SD% 4.192±0.033 22.790±0.171 RSD%* 0.780 0.751 Protein Factor： 5.18 for almonds and 5.46 for peanuts *RSD% =(Standard Deviation * 100)/ Average The complete procedure was verified by using 5 ml of glycine standard solution (3%) containing 28 mg of nitrogen asreference substance. The obtained recovery falls into the expected range： between 98%and 102 %. Conclusions The obtained results are reliable and reproducible in accordance with the expected values： all data fulfill the expectedrange. Benefits of Kjeldahl method by using DKL 20 and UDK 169 with AutoKjel Autosampler are： High level of precision and reproducibility Maximum productivity and full automation Worldwide official method Reliable and easy method Time saving e Moderate running costs Copyright C VELP Scientifica. All rights reserved.No part of this publication may be reproduced or transmitted in any form or for any purpose without the express permission of VELP.VELP Scientifica， Italy Tel： + Fax： + www.velp.com