I want to thank Pat Bull for her thoughtful and professional
discussion of milk storage considerations.  I am not aware of any studies
examining nylon lined milk storage bags, however there is one old reference
in which the author suggests they are responsible for greater retrieval of
viable cells after storage (19% retrieval of viable cells after 4 weeks of
frozen storage at -23 degrees C).  The author also attributed reduced fat
adhesion to the use of these bags.  The reference is:  Reynolds, GJ et al. A
simplified system of human milk banking.  Early Human Development.
1982;7:281.
      The time, temperature, and storage container have been shown to affect
not only specific (as opposed to non-specific) secretory IgA, but also
vitamin C, lysozyme, lactoferrin, phagocytic activity of milk leucocytes,
free fatty acids and lipid peroxidation. Much of this work was done in the
early 1980s as a part of a concerted effort to identify appropriate
protocols for banking human milk for premature infants and for research.  A
concise review of the findings of this series of studies may be found in the
Journal of the American College of Nutrition. 1984; vol 3, pages 123-129. in
an article by Garza and Nichols titled "Studies of Human Milk Relevant to
Milk Banking".  This article is interesting historically as well as
scientifically since it refers to the use of 'drip milk' (remember when?)
for feeding premature infants.  These studies are old, but it may be a while
before that level of funding is again directed toward a comprehensive
analyses of changes in human milk during storage.
        A more recent article relating to milk storage which has received
little attention is:  van Zoeren-Grobben, Moison, Ester and Berger. "Lipid
peroxidation in human milk and infant formula: effect of storage, tube
feeding and exposure to phototherapy". Acta Paediatr. 1993;82:645-9. Here is
a quote:  "Storage of human milk (+4 C for four days) increased lipid
peroxidation.  Exposure to light during tube feeding increased peroxidation
in infant formula but not in human milk."  In all cases more peroxidation
products were present in formula, but handling of the milk influenced it's
level relative to fresh milk.  No comparisons with frozen samples were made.
(However,lower temperatures generally retard enzymatic activity.)
Peroxidized lipids have been suggested to play a role in the pathogenesis of
necrotizing enteocolitis and bronchopulmonary dysplasia in premature
infants.