On food and cooking the science and lore of the kitchen ( PDFDrive ) 41
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orangeprecursorsthecarotenes,whichare
foundingreenfeedandgivemilkandundyed
butterwhatevercolortheyhave.Breedsdiffer
intheamountofcarotenetheyconvertinto
vitaminA;GuernseyandJerseycowsconvert
littleandgiveespeciallygoldenmilk,whileat
theotherextremesheep,goats,andwater
buffaloprocessnearlyalloftheircarotene,so
theirmilkandbutterarenutritiousbutwhite.
Riboflavin,whichhasagreenishcolor,can
sometimesbeseeninskimmilkorinthe
waterytranslucentwheythatdrainsfromthe
curdledproteinsofyogurt.
MilkSugar:Lactose
Theonlycarbohydratefoundinanyquantity
inmilkisalsopeculiartomilk(andahandful
ofplants),andsowasnamedlactose,or“milk
sugar.”(Lac-isaprefixbasedontheGreek
wordfor“milk”;we’llencounteritagainin
thenamesofmilkproteins,acids,and
bacteria.)Lactoseisacompositeofthetwo
simplesugarsglucoseandgalactose,which
arejoinedtogetherinthesecretorycellofthe
mammarygland,andnowhereelseinthe
animalbody.Itprovidesnearlyhalfofthe
caloriesinhumanmilk,and40%incow’s
milk,andgivesmilkitssweettaste.
Theuniquenessoflactosehastwomajor
practicalconsequences.First,weneeda
specialenzymetodigestlactose;andmany
adultslackthatenzymeandhavetobecareful
aboutwhatdairyproductstheyconsume(p.
14).Second,mostmicrobestakesometimeto
maketheirownlactose-digestingenzyme
beforetheycangrowwellinmilk,butone
grouphasenzymesatthereadyandcangeta
headstartonalltheothers.Thebacteria
knownasLactobacilliandLactococcinot
onlygrowonlactoseimmediately,theyalso
convertitintolacticacid(“milkacid”).They
thusacidifythemilk,andinsodoing,makeit
lesshabitablebyothermicrobes,including
