National Research Council over ruwe as
“The minerals present in a feed are found mainly in the ash component when the feed is analyzed… The ash consists of oxides, phosphates, carbonates and sulfates of minerals (inorganix elements) including calcium, phosphorus, magnesium, sodium, potassioum, iron, copper, manganese and zinc. Other minerals such as chloride, iodine, sulfur and selenium may be partially or totally lost in the form of gaseous compounds during the combustion process.”
Bron: National Research Council. Hoofdstuk 7. Nutrient requirements of dogs and cats. National Academies Press, 2006.
De relatie ruwe as – bot – calcium
“The intercorrelations of bone, ash, and calcium contents have been analyzed by Field, who proposes respective conversion factors mined directly to ash or calcium content. For exact results it is neessary to determine specific conversion factors adapted to the repective material. Generally only calcium content is used as a parameter for the indirect determination of bone content. (het gaat hier over het vaststellen van de hoeveelheid calcium in een vleesproduct, om te kunnen zien of er ook bot inzit) In pure muscle tissue, calcium content generally does not exceed 0,0008%, while the ash content is in the order of magnitude of 1%.
…
“Mammal species have a higher ash and calcium content than poultry. Ash and calcium contents increase considerably with age. Also bone type has a major effect” Femurs and other long bones have a higher ash content. “If calcium is related to bone ash, this calcium content of ash is remarkably constant at 36,5%-38,5% (37% average). The standard error within animal species is largely no more than 1%. This constancy led Arneth to define calcium content of bone ash as most adequate for the presentation of calcium analysis results. It is less useful to relate calcium content to fresh bone weight, which varies more than dry bone weight and may be biased by preparation.”
Calcium is a rather constant fraction of bone ash: 37%.
Bron: Toldrá, Fidel. “Chapter 15.5 Indirect Detection of Bone Components in Meat.” Handbook of Analysis of Edible Animal By-products. Boca Raton, FL: CRC, 2011. Pagina 271, en 275.
De manieren van ruwe as vaststellen: dry ashing en wet ashing
Er zijn twee manieren van het vaststellen van de hoeveelheid ruwe as: dry ashing en wet ashing. Bij dry ashing wordt de voeding in een oven gedaan en voor 12 tot 18 uur lang op ongeveer 550 graden celcius verbrand. Water en vluchtige stoffen verdampen en de meeste mineralen worden omgezet tot oxides, sulfaten, chlorides en silicaten. Elementen zoals ijzer, selenium en lood kunnen deels vervliegen tijdens deze procedure. Als het doel van het ‘ashen’ is om specifieke mineralen te analyseren, wordt deze manier dus niet gebruikt.
Bij wet ashing wordt er gebruik gemaakt van zuren en/of oxiderende ‘agents’, waardoor geen vervlieging plaatsvindt.
“Ash contents represent the total mineral content in foods.”
Bron: Nielsen, Suzanne. “Hoofdstuk 7 Ash Analysis”, Food analysis 4th edition, 2010. (In te zien via Google Books en te downloaden als pdf)